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Article Cite This: J. Org. Chem. 2018, 83, 1204−1215

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Switchable Chemoselective Transfer Hydrogenations of Unsaturated Carbonyls Using Copper(I) N‑Donor Thiolate Clusters Meng-Juan Zhang,†,⊥ Da-Wei Tan,†,⊥ Hong-Xi Li,*,†,‡ David James Young,§ Hui-Fang Wang,*,† Hai-Yan Li,† and Jian-Ping Lang*,†,‡ †

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123 Jiangsu, People’s Republic of China ‡ State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China § Faculty of Science and Engineering, University of the Sunshine Coast, Maroochydore DC, Queensland 4558, Australia S Supporting Information *

ABSTRACT: Unsaturated alcohols and saturated carbonyls are important chemical, pharmaceutical, and biochemical intermediates. We herein report an efficient transfer hydrogenation protocol in which conversion of unsaturated carbonyl compounds to either unsaturated alcohols or saturated carbonyls was catalyzed by Cu(I) N-donor thiolate clusters along with changing hydrogen source (isopropanol or butanol) and base (NaOH or K2CO3). Mechanistic studies supported by DFT transition state modeling indicate that such a chemoselectivity can be explained by the relative concentrations of Cu(I) monohydride and protonated Cu(I) hydride complexes in each catalytic system.

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INTRODUCTION

We have a long-standing interest in the synthesis and catalytic properties of Cu(I) N-heterocycle thiolate clusters.79,80 These complexes are attractive candidates for the chemoselective transfer hydrogenation of unsaturated carbonyls to both allylic alcohols and saturated carbonyls because (i) thiolate ligands can stabilize Cu(I) hydride catalysts,81,82 (ii) Cu(I) thiolates display high catalytic activity,83 (iii) copper nanoparticles (CuNPs) are active for the transfer hydrogenation of carbonyl compounds84,85 but show poor chemoselectivity in the presence of CC, CN, and NN bonds,85 and (iv) Ndonor thiols such as pyrimidine-2-thiol are relatively nontoxic ligands that bind metal ion as the neutral thione or anionic thiolate.79,80,83,86−91 This dual coordinating ability could potentially form dual-acting catalytic intermediates (Scheme 1). Can the two active species transfer hydrogenate unsaturated carbonyls with CC bond54−63 reduction or CO bond64−78 reduction? We herein report that indeed Cu(I) N-heterocycle thiolate clusters efficiently mediate the chemoselective transfer hydrogenation of unsaturated carbonyl compounds to either unsaturated alcohols or saturated carbonyls by a simple manipulation of reaction conditions.

The chemoselective hydrogenation of unsaturated aldehydes and ketones to generate allylic alcohols1−4 or saturated carbonyl compounds5−7 is an important transformation in organic synthesis, pharmaceutical chemistry, and biochemistry.8−11 Considerable efforts have been devoted to selective heterogeneous and homogeneous catalytic reductions using flammable hydrogen gas,12−15 costly hydrosilanes,16−20 borohydrides,21−23 Hantzsch esters,24−26 and so forth27−32 as reducing agents. The selectivity of hydrogenation is influenced by the metal center, organic ligand, structure, texture, and composition of the catalyst (particle size, shape, support, and molar ratio of components), reaction conditions (temperature, pressure, and solvent), and substituents on the substrates.33−43 Catalytic transfer hydrogenation using benign alcohols as hydride sources represents an attractive alternative to these methods in terms of atom economy and environmental impact.44−53 Metal hydride species generated from molecular Pd,54−56 Ir,57−59 Ru,60,61 Ni62 complexes, preferentially transfer hydrogenate the CC bond of unsaturated carbonyls to saturated carbonyl compounds. By comparison, metal−ligand bifunctional H−M−NH catalysis, pioneered by Noyori’s group,63,64 provides an efficient chemoselective transfer hydrogenation of CO bonds in unsaturated carbonyl compounds.66−78 Chemoselective access to both unsaturated alcohols and saturated carbonyls with a single catalyst has hitherto not been achieved. © 2018 American Chemical Society

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RESULTS AND DISCUSSION A series of Cu(I) N-heterocycle thiolate complexes [Cu3(pymt)3]n (1a)87,88 and [Cu6(L)6] (L = btt (1b),89 pyt Received: October 23, 2017 Published: January 9, 2018 1204

DOI: 10.1021/acs.joc.7b02676 J. Org. Chem. 2018, 83, 1204−1215

Article

The Journal of Organic Chemistry Scheme 1. Structures of Cu(I) N-Heterocycle Thiolate Complexes and Possible Dual-Acting Hydride Species for Hydrogenation of Unsaturated Carbonyl Compounds

Scheme 2. Structures of Complexes 1a−1i

(1c),90 dmpymt (1d),91 5-phpymt (1e),80 mtpmt (1f),79 4phpymt (1g), 4,5-diphpymt (1h)) were prepared by reaction of CuI with excess pyrimidine-2-thiol (Hpymt), 2-benzothiazolethiol (Hbtt), pyridine-2-thiol (Hpyt), 4,6-dimethylpyrimidine2-thiol (Hdmpymt), 5-phenylpyrimidine-2-thiol (5-Hphpymt), 4-phenylpyrimidine-2-thiol (4-Hphpymt), 5-methyl-4-(p-tolyl)pyrimidine-2-thiol (Hmtpmt), or 4,5-diphenylpyrimidine-2thiol (4,5-Hdiphpymt) in the presence of Et3N. Solvothermal reaction of CuI with 4,6-diphenyl-5,6-dihydropyrimidine2(1H)-thione (4,6-H3diphpymt) produced [Cu6(4,6-diphpymt)6] (1i, 4,6-Hdiphpymt = 4,6-diphenylpyrimidine-2thiol). In this reaction, 4,6-H3diphpymt was oxidized to the 4,6-diphpymt− ligand in situ (Scheme 2). The structures of 1g− 1i (Figures S1−S3) resemble those of 1b−1f.79,80,89−91 Six Cu(I) atoms are connected by six 4-phpymt, 4,5-diphpymt, or 4,6-diphpymt ligands to yield a hexanuclear structure. With these as-prepared copper(I) N-donor thiolate clusters 1a−1i in hand, we examined their catalytic activities toward the transfer hydrogenation reduction of cinnamaldehyde (2aa) with propan-2-ol (i-PrOH) as both the hydrogen source and solvent (Table 1). The hydrogenation of 2aa could occur at CO and/or CC bonds to afford cinnamic alcohol (3aa), 3phenylpropanal (4aa), and 3-phenylpropan-1-ol (5aa). We first carried out the reaction of 2aa (1.0 mmol) with 1a (5 mol % of Cu) and NaOH (20 mol %) in 4 mL of i-PrOH at 100 °C. After 10 h, the 90% conversion of 2aa was achieved, and the selectivity for 3aa was 84% in the final product distribution. As presented in Table 1, 1a−1i selectively reduced the CO bond prior to the reduction of the CC bond (entries 1−9). Among these catalysts, 1d displayed the highest activity and selectivity, giving an almost quantitative conversion to 3aa with

98% selectivity (entry 4). By comparison, [CuI(bpy)]2 (bpy = 2,2′-bipyridine), [CuI(phen)]2 (phen = 1,10-phenanthroline), and CuI (entries 10−12) exhibited much lower catalytic activity and chemoselectivity than these Cu clusters. The blank reaction using only NaOH without catalyst proceeded in 13% conversion (entry 13), which was ascribed to the base-catalyzed Meerwein−Pondorf−Verley (MPV-O) reduction.92−94 These results indicated that Cu(I) N-heterocycle thiolate complexes were responsible for the hydrogen transfer reaction and that the N-donor thiolate ligands exerted a significant impact on their catalytic activity. Therefore, 1d and 2aa were chosen as a model system to optimize the reaction conditions such as base, solvent, and temperature. Base played a critical role in catalytic hydrogenation and the product distribution (entries 14−22). NaOH proved excellent conversion with superior selectivity (entry 4). The use of t-BuONa or t-BuOK as a base gave complete conversion of 2aa but with lower selectivity for 3aa than NaOH (entries 14 and 15). When KOH, LiOH, or Cs2CO3 was used as a base, the conversions of 2aa were 89− 98% with 53−92% selectivity of 3aa (entries 16−18). Surprisingly, weak bases such as K2CO3 and K3PO4 (entries 19 and 20) exhibited reduced activity and lower selectivity, and Na2CO3 was almost inactive (entry 21). Cluster 1d did not work without the addition of base (entry 22). A decreased proportion of NaOH (10 mol %) led to a lower catalysis performance (entry 23), but beyond this amount (20 mol %), the selectivity of 3aa actually decreased to 90 and 85% for stoichiometries of 50 and 100 mol %, respectively (entries 24 and 25). At lower temperatures (80 °C), the reaction proceeded in a commensurate yield (entry 26). Compound 1d also showed high activity but with moderate selectivity for 1205


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The Journal of Organic Chemistry Table 1. Optimizing Reaction Conditions for the Transfer Hydrogenation Reduction of 2aa

yieldb a

entry

cat.

base

solvent

conversion

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23c 24d 25e 26f 27 28 29

1a 1b 1c 1d 1e 1f 1g 1h 1i CuI [CuI(phen)]2 [CuI(bpy)]2

NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH t-BuONa t-BuOK KOH LiOH Cs2CO3 K3PO4 K2CO3 Na2CO3

i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH i-PrOH MeOH EtOH n-BuOH

90% 97% 88% >99% 94% 89% 95% 93% 94% 32% 47% 51% 13% >99% >99% 98% 97% 89% 20% 15% 99% 79% 96% 97% >99%

1d 1d 1d 1d 1d 1d 1d 1d 1d 1d 1d 1d 1d 1d 1d 1d

NaOH NaOH NaOH NaOH NaOH NaOH NaOH

b

3aa

4aa

5aa

84% 92% 83% 98% 85% 79% 87% 81% 83% 42% 38% 44% 45% 78% 62% 72% 92% 53% 52% 42%

7% 6% 9% 2% 8% 12% 7% 9% 9% 28% 35% 32% 23% 22% 17% 10% 2% 6% 22% 21%

9% 2% 8% trace 7% 9% 6% 10% 8% 30% 27% 24% 32% trace 21% 18% 6% 41% 26% 37%

94% 90% 85% 95% 45% 59% 52%

4% 4% 7% 3% 17% 8% 42%

2% 6% 8% 2% 38% 33% 6%

Reaction conditions: 2aa (1.0 mmol), base (0.20 mmol), cat. (5 mol % of Cu), i-PrOH (4 mL) at 100 °C (oil bath) for 10 h under a N2 atmosphere. bConversion and selectivity determined by HPLC. cUsing 0.10 mmol NaOH. dUsing 0.50 mmol NaOH. eUsing 1.0 mmol NaOH. fAt 80 °C. a

3aa (45−59%) in MeOH, EtOH, and 1-butanol (n-BuOH) (entries 27−29). The selectivity of 5aa in MeOH and EtOH increased. The yield of 4aa increased from 2% in i-PrOH to 42% in n-BuOH. The chemoselective transfer hydrogenation could be best achieved in i-PrOH as a solvent and hydrogen agent using 1d (5 mol % Cu) as a catalyst and 20 mol % NaOH as a base at 100 °C within 10 h. With the optimized conditions established, we next investigated the substrate scope of unsaturated carbonyl complexes (Table 2). The transfer hydrogenation reactions proceeded well for all substrates examined, and the desired unsaturated alcohols were isolated in good to excellent yields with high chemoselectivity. Aromatic α,β-unsaturated aldehydes (2aa−2ae, entries 1−5) typically exhibited higher activity than the corresponding aliphatic unsaturated aldehydes 2ag and 2ah (entries 7 and 8). The reduction of heteroatom-containing α,βunsaturated aldehydes resulted in CO bond-selective hydrogenation to 3af and 3ai−3ak (entries 6 and 9−11) in moderate yields. Higher yields of 74−80% for these substrates could be achieved by prolonging the reaction time to 36 h. Unsaturated ketones required longer time for the transfer hydrogenation reactions to complete the conversions. Substrates 2al−2ap (entries 12−16) afforded excellent yields of the desired

secondary alcohols 3al−3ap with retention of the olefinic bond (82−93% yields). The above results revealed that 1d easily catalyzed the chemoselective transfer hydrogenation of the CO bond of conjugated or unconjugated unsaturated carbonyls to unsaturated alcohols. The hydrogenation of chalcones 2ba, 2bb, 2ca−2cc (entries 17−21) gave the corresponding unsaturated alcohols 3ba, 3bb, and 3ca−3cc in 87−93% isolated yields. The formation of a trace amount of saturated aldehyde 4aa in the reduction of 2aa inspired us to further investigate the selective synthesis of saturated carbonyl compounds. Table 1 also showed that base and solvent (or hydrogen agent) did exert a significant impact on the chemoselectivity. The use of 1b (10 mol % Cu) as catalyst, equimolar K2CO3 as base, nBuOH (2 mL) as hydride source and solvent (Table S1) produced saturated carbonyl compounds in excellent yield and high selectivity (Table 3). Both electron-donating and -withdrawing aromatic-substituted chalcones were hydrogenated to cleanly provide the corresponding ketones 4ba−4be and 4ca− 4ce (entries 1−5 and 9−13). The position of the substituent groups on the benzene rings did not significantly affect the yield. The chalcones with substituents at the 2- or 3-positions gave good yields of products 4bf, 4cf, and 4cg (entries 6, 14, 1206


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The Journal of Organic Chemistry

and 15). To our delight, heterocyclic α-enones exhibited good activity and high selectivity (4bg, 4bh, 4ch, 4ci, entries 7, 8, 16, and 17). Likewise, the transfer hydrogenation of alkylsubstituted α-enones proceeded smoothly (4cj and 4ck, entries 18 and 19). However, good conversion and lower selectivity for unsaturated aldehyde 2aa were observed. Saturated aldehyde 4aa was isolated in 51% yield under the optimized conditions (entry 20). A previous investigation using copper nanoparticles to catalyze selective transfer hydrogenation indicated that high yield with high selectivity is very challenging with this inexpensive metal.85 Cu(I) N-donor thiolate complexes displayed excellent selectivity toward unsaturated alcohols or saturated ketones under the different optimized conditions. For better understanding of the reasons for this switch in selectivity with hydride source and base, we acquired the 1H NMR spectrum of 1d in CDCl3 in the presence and absence of the relevant reagents. The 1H NMR spectrum of 1d exhibited two sets of aromatic resonances (at δ 6.67, 6.30 ppm) in a 1:0.11 ratio and two sets of methyl resonances (at δ 2.52/2.39, 2.31 ppm) in a 1:0.24 ratio (Figure S4). Approximately 90% of dmpymt kept μ3-κ(N):κ2(S) coordination in CDCl3, whereas 10% of this ligand coordinated with Cu(I) in μ−κ2(S) fashion. When NaOH was added to the CDCl3 solution of 1d at room temperature, no change in the 1H NMR spectrum was observed. However, the proton resonances of dmpymt showed small upfield shifts to δ 6.64, 6.27, 2.47/2.34, and 2.27 ppm when i-PrOH was added to the CDCl3 solution of 1d. We attribute these changes to hydrogen bonding interactions of the pyrimidyl ring N atoms with i-PrOH molecules.80 Subsequent addition of NaOH increased the ratio of monodentate dmpymt up to ∼30%, which we suggest is caused by the coordination of i-PrO− to the Cu(I) center. After the catalytic reaction of cinnamaldehyde as substrate, the resulting mixture was dried under vacuum and then washed with Et2O several times. The 1 H NMR spectrum of the residue was very similar to that of 1d. This residue could be reused and displayed high activity and selectivity for the reduction of 2aa, giving 3aa in 91% yield. We propose that the mechanism leading to each product outcome involves either the sequential hydride transfer from a copper hydride intermediate (Cat I, Scheme 3) followed by protonation or concerted hydride/proton transfer from protonated Cu(I) hydride species Cat II. Cat I is formed by the β-elimination of acetone from Cu isopropoxide intermediate (I) and Cat II by protonation of Cat I with alcohol. A Cat I-like Cu(I) hydride species has been reported previously.87 Hydrogenation at the CO or CC bonds of 2aa with Cat I resulted in the formation of 3-phenylprop-2-en-1-olate and 1oxo-3-phenylpropan-2-ide anions, respectively. They then were protonated by i-PrOH to produce 3-phenylprop-2-en-1-ol (3aa) or 3-phenylpropanal (4aa), respectively. To isolate the factors responsible for the switching reduction pathways, we carried out the reaction of 2aa with i-PrONa as a hydride source and base but in the absence of a proton source in toluene at 90 °C. Hydrogenation of the CC bond under these conditions was highly preferred over reduction of the CO bond (Table 4), presumably via the intermediacy of Cat I. If we invoke a metal−ligand bifunctional mechanism,64−78 the proton from propan-2-ol is delivered to the dmpymt ligand, yielding a hydride/proton complex (Cat II), and there exists three possible hydrogenation products of 2aa (3aa, 4aa, and 3phenylprop-1-en-1-ol) (Scheme 3). Compound 3-phenylprop-

Table 2. Transfer Hydrogenation of Unsaturated Carbonyls to Allylic Alcohols

a

Reaction conditions: unsaturated ketone or aldehyde (1.0 mmol), NaOH (0.2 mmol), 1d (5 mol % Cu), i-PrOH (4 mL) at 100 °C (oil bath) under N2. bData determined by HPLC with biphenyl as an internal standard. cIsolated yield. 1207


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The Journal of Organic Chemistry Table 3. Transfer Hydrogenation of Unsaturated Carbonyls to Saturated Carbonyls

Reaction conditions: unsaturated carbonyl (0.5 mmol), K2CO3 (0.5 mmol), 1b (10 mol % Cu), n-BuOH (2 mL) at 120 °C (oil bath) under N2 for 24 h. bData determined by HPLC with biphenyl as an internal standard. cIsolated yield. dThe hydrogenation of 2aa with 90% conversion gave 4aa in 51% yield, 3aa in 38% yield, and a trace of 5aa. a

through the interaction of the Cu−H of “(dmpymt)Cu−H” with the CO or CC bond (Figure S5). The CO and CC hydrogenations have barriers of 16.9 and 16.1 kcal mol−1, respectively. This energy barrier difference increased to 3.6 kcal mol−1 when the LANL2TZ basis set was used for the Cu atom. This calculation supports our hypothesis that monohydride Cu(I) complex Cat I preferentially hydrogenates the CC bond of unsaturated aldehydes or ketones. There are two hydrogenation routes (1,2-, and 1,4-addition) for the reaction of 2aa with protonated Cu(I) hydride species “(Hdmpymt)Cu−H”. The calculated free energy diagram indicates that the 1,2-addition pathway involves two transition states (TS1, TS2) (Figure S6) with the higher energy barrier of 10.6 kcal mol−1 (TS1). The 1,4-addition pathway involves the insertion of Cu−H into the CC bond via three consecutive transition states (TS3, TS4, and TS5) (Figure S7). The highest energy barrier (TS4) is calculated to be 15.3 kcal mol−1. The calculated energy difference between TS4 and TS1 is 1.06 kcal mol−1 when chalcone 2ba is used as a substrate. These findings are in agreement with the experimentally observed formation of unsaturated alcohol using 20 mol % NaOH as a base in i-PrOH.

1-en-1-ol is the tautomer of saturated aldehyde 4aa. To investigate the role of the NH or SH group, we modified Hdmpymt by methylation and phenylation to obtain two new ligands 4,6-dimethyl-2-(methylthio)pyrimidine (dmmtpym) and 4,6-dimethyl-1-phenylpyrimidine-2(1H)-thione (dmphpymt), neither of which have a basic nitrogen for protonation. The resulting two Cu(I) complexes [CuI(L)] (L = dmmtpym, dmphpymt) and [Cu(SPh)] exhibited reduced activity and selectivity (Table 4). All of these results support the idea of an NH (or SH) proton transfer concomitant with carbonyl reduction by Cu−H. Density functional theory (DFT) calculations modeling the hydrogenation of 2aa with a simplified “Cu(dmpymt)” unit were in agreement with our experimental observations (Supporting Information). The B3LYP hybrid functional was used in our calculations. The LANL2DZ basis set, in conjunction with the LANL2DZ pseudo potential, was employed for copper, whereas the 6-311++G(d,p) basis set was used for other atoms. Frequency analyses were performed on all optimized structures to verify local minima or transition states. All calculated results were based on Gibbs free energies. We first examined the hydrogenation of cinnamaldehyde 1208


Article

The Journal of Organic Chemistry Scheme 3. Possible Routes for the Hydrogenation of 2aa Using 1d

Table 4. Transfer Hydrogenation of 2aa Under the Different Reaction Conditions

yield

a b

entry

cat.

base

solvent

time

1a 2a 3a 4b 5b 6b

1d 1d 1d [CuI(dmmtpym)] [CuI(dmphpymt)] [Cu(SPh)]

i-PrONa i-PrONa i-PrONa NaOH NaOH NaOH

toluene toluene toluene i-PrOH i-PrOH i-PrOH

6 12 24 24 24 24

h h h h h h

3aa

4aa

5aa

52% 56% 30%

12% 20% 38% 9% 8% 13%

trace trace 5% 8% 8% 12%

Reaction conditions: 2aa (1.0 mmol), i-PrONa (1.0 mmol), 1d (10 mol % Cu), toluene (4 mL) at 90 °C (oil bath) under N2 and HPLC yield. Reaction conditions: 2aa (1.0 mmol), NaOH (0.2 mmol), cat. (10 mol % Cu), i-PrOH (4 mL) at 100 °C (oil bath) under N2 and HPLC yield.

The distribution of products derived from the hydrogenation of 2aa with 5 mol % 1d in i-PrOH and 20 mol % NaOH as base was monitored over time using HPLC (Figure 1(a)) and revealed the initial generation of unsaturated alcohol 3aa over 3 h. A small amount of 3-phenylpropan-1-ol (5aa) was also formed and then replaced by 3-phenylpropanal (4aa, ∼2% HPLC yield). This observation of the clean first-order generation of allylic alcohol with no observable intermediates or significant other products is consistent with our proposed outer-sphere hydrogen transfer mechanism catalyzed by protonated Cu(I) hydride Cat II (Schemes 3 and 4). In this catalytic process, the concentration of unprotonated monohydride Cu(I) complex Cat I is relatively low due to the catalytic (20%) amount of base. The conversion of 2aa had a

turnover number (TON) of 19.6 and a turnover frequency (TOF) as high as 2.86 h−1, whereas the selectivity was 98% for the production of 3aa. The catalytic activity of complex 1d is higher than that of [(Ph3P)CuH]6/PhP(CH2)4 (TON = 17.6, TOF = 0.98 h−1) but lower than that of [(Ph3P)CuH]6/ PhPMe2 (TON = 18.6, TOF = 4.6 h−1) (using 500 psi H2 as hydrogen agent).1 As discussed above, 1d showed lower selectivity (Table 1, entries 27−29) in ROH (R = Me, Et, n-Bu) than in i-PrOH, which may be due to the fact that the smaller size of R in ROH favors Cat I to hydrogenate the CC bond. The selective transfer hydrogenation of α,β-unsaturated ketone 2ba to saturated ketone 4ba was also monitored over time using HPLC as shown in Figure 1(b). Unsaturated alcohol 3ba was formed initially, concomitant with a sharp decrease in 1209


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Figure 1. Time-course monitoring of the transfer hydrogenation of 2aa in i-PrOH (a) and 2ba in n-BuOH (b).

Scheme 4. Proposed Mechanism for the Transfer Hydrogenation of Unsaturated Carbonyls to Unsaturated Alcohols or Saturated Carbonyls

Scheme 5. Reaction of 3ba or 5ba Catalyzed by 1b in n-BuOH

system without the formation of H2O, which can hydrogen interact with the N atom in Cat I. The reaction of 5ba under standard conditions could not yield 4ba (eq 2). The addition of n-butanal into the reaction system increased the yield of 4ba to 81% (eq 3). Thus, the transformations from unsaturated carbonyls into saturated carbonyls proceeded through a onepot sequence of the hydrogenation of CO bond, the hydrogenation of CC bond, and transfer hydrogen of saturated alcohol with n-butanal (Schemes 3 and 4).

the concentration of 2ba, and then replaced by saturated alcohol 5ba. The increase in base raised the concentration of monohydride species Cat I, which resulted in the CC hydrogenation of 3ba to give 5ba. Compound 5ba was subsequently oxidized to 4ba. In a separate experiment, the reaction of 3ba for 5 h under the same conditions resulted in the formation of 4ba in 48% yield coupled with saturated alcohol 5ba in 21% yield (Scheme 5, eq 1). Compared with NaOH and KOH, K2CO3 and K3PO4 as bases displayed higher chemoselectivities for saturated carbonyls (Table S1). These bases could increase the concentration of Cat I in the catalytic 1210


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CCD (1h·4CHCl3) diffractometer using graphite-monochromated Mo Kα (λ = 0.71070 Å) radiation. The crystal structures of 1g·2DMF· Et2O, 1h·4CHCl3, and 1i were solved by direct methods and refined on F2 by full-matrix least-squares techniques with the SHELXTL-97 program.95,96 Crystal structural data for 1g·2DMF·Et2O, 1h·4CHCl3, and 1i (CCDC 1522340−1522342) are contained in the respective CIFs. Computational Details. Geometry optimizations were performed at a mixed basis set (LANL2DZ for copper atom and 6-311++G(d,p) for other atoms) using the B3LYP functional97 in Gaussian 09.98 Transition states were optimized with the Berny algorithm using GEDIIS in redundant internal algorithm. Analytical frequencies were calculated at the same theoretical level to obtain Gibbs free energies and to verify a local minimum or transition state. Transfer Hydrogenation of Unsaturated Carbonyls to Unsaturated Alcohols. In a typical procedure, a test tube equipped with a magnetic stirring bar was charged with unsaturated carbonyl (1.0 mmol), NaOH (0.20 mmol), 1d (5 mol % Cu), and i-PrOH (4 mL) and then sealed. The reaction mixture was stirred at 100 °C. After cooling to room temperature, the mixture was partitioned between water and ethyl acetate. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate (3 × 15 mL). The combined organic layer was washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure. The crude product was purified by flash column chromatography. Cinnamic Alcohol (3aa).15 Yield: 126 mg (94%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.38 (d, J = 7.4 Hz, 2H), 7.31 (t, J = 7.4 Hz, 2H), 7.24 (dd, J = 8.8, 5.2 Hz, 1H), 6.61 (d, J = 15.9 Hz, 1H), 6.36 (dt, J = 15.8, 5.7 Hz, 1H), 4.31 (d, J = 5.5 Hz, 2H), 1.75 (d, J = 7.9 Hz, 1H). 13C NMR (151 MHz, CDCl3, ppm): δ 136.6, 131.1, 128.6, 128.5, 127.7, 126.4, 63.7. HRMS m/z calcd for C9H10O [M + H]+ 135.0810, found 135.0811. 4-Methoxycinnamic Alcohol (3ab).77 Yield: 157 mg (96%). 1H NMR (400 MHz, DMSO-d6, ppm): δ 7.35 (d, J = 8.2 Hz, 2H), 6.88 (d, J = 8.2 Hz, 2H), 6.48 (d, J = 15.9 Hz, 1H), 6.21 (dt, J = 15.8, 5.1 Hz, 1H), 4.80 (t, J = 5.3 Hz, 1H), 4.09 (t, J = 4.8 Hz, 2H), 3.74 (s, 3H). 13C NMR (151 MHz, DMSO-d6, ppm): δ 158.6, 129.5, 128.3, 128.2, 127.3, 114.0, 61.6, 55.0. HRMS m/z calcd for C10H13O2 [M + H]+ 165.0916, found 165.0918. 4-Nitrocinnamic Alcohol (3ac).77 Yield: 161 mg (90%). 1H NMR (400 MHz, CDCl3, ppm): δ 8.19 (d, J = 8.5 Hz, 2H), 7.52 (d, J = 8.5 Hz, 2H), 6.72 (d, J = 16.0 Hz, 1H), 6.54 (dt, J = 15.9, 4.9 Hz, 1H), 4.41 (d, J = 4.4 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 146.9, 143.2, 133.5, 128.3, 126.9, 124.0, 63.1. HRMS m/z calcd for C9H9NO3 [M + H]+ 180.0661, found 180.0662. α-Methylcinnamic Alcohol (3ad).15 Yield: 136 mg (92%). 1H NMR (600 MHz, CDCl3, ppm): δ 7.32 (t, J = 7.5 Hz, 2H), 7.27 (d, J = 7.7 Hz, 2H), 7.22 (dd, J = 14.4, 7.1 Hz, 1H), 6.52 (s, 1H), 4.17 (s, 2H), 1.89 (s, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 137.7, 137.8, 129.0, 128.2, 126.5, 125.1, 69.0, 15.4. HRMS m/z calcd for C10H12O [M + H]+ 149.0966, found 149.0966. α-Amylcinnamic Alcohol (3ae).15 Yield: 186 mg (91%). 1H NMR (600 MHz, CDCl3, ppm): δ 7.32 (t, J = 7.6 Hz, 2H), 7.25−7.20 (m, 3H), 6.52 (s, 1H), 4.22 (s, 2H), 2.30−2.27 (m, 2H), 1.62 (s, 1H), 1.52−1.47 (m, 2H), 1.31−1.26 (m, 4H), 0.87 (t, J = 6.6 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 142.5, 137.7, 128.8, 128.3, 126.6, 125.4, 67.2, 32.2, 28.9, 28.2, 22.6, 14.2. HRMS m/z calcd for C14H20O [M + H]+ 205.1592, found 205.1594. 3-(Furan-2-yl)prop-2-en-1-ol (3af).15 Yield: 109 mg (88%). 1H NMR (600 MHz, CDCl3, ppm): δ 7.33 (s, 1H), 6.42 (d, J = 15.9 Hz, 1H), 6.37−6.34 (m, 1H), 6.27 (dt, J = 15.8, 5.6 Hz, 1H), 6.22 (d, J = 3.0 Hz, 1H), 4.26 (d, J = 5.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 152.5, 142.1, 127.3, 119.3, 111.4, 108.0, 63.2. HRMS m/z calcd for C7H8O2 [M + H]+ 125.0603, found 125.0604. Hept-2-en-1-ol (3ag).15 Yield: 99 mg (87%). 1H NMR (600 MHz, CDCl3, ppm): δ 5.71−5.64 (m, 1H), 5.64−5.58 (m, 1H), 4.06 (d, J = 4.9 Hz, 2H), 2.03 (q, J = 6.7 Hz, 2H), 1.36−1.28 (m, 4H), 0.88 (t, J = 7.1 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 133.6, 128.9, 63.9, 32.0, 31.4, 22.3, 14.0. HRMS m/z calcd for C7H14O [M + H]+ 115.1123, found 115.1126.

CONCLUSIONS In summary, we have developed an efficient and chemoselective transfer hydrogenation protocol for converting unsaturated carbonyl compounds to either unsaturated alcohols or saturated carbonyls catalyzed by Cu(I) N-donor thiolate clusters using either i-PrOH as the hydrogen source and 20 mol % NaOH as base or n-BuOH and equimolar K2CO3. This chemoselectivity can be explained by the relative concentrations of Cu(I) monohydride and protonated Cu(I) hydride complexes in each catalytic system. These clusters may also effectively mediate the α-alkylation of acetophenones with primary alcohols, and these studies are currently under way in our laboratory.

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EXPERIMENTAL SECTION

General Information. [Cu3(pymt)3]n (1a)87,88 and [Cu6(L)6] (L = btt (1b),89 pyt (1c),90 dmpymt (1d),91 5-phpymt (1e),80 mtpmt (1f)79) were prepared according to literature methods. All reagents were obtained from commercial sources and used directly without further purification. All solvents were obtained from commercial sources and purified according to standard procedures. Column chromatography was performed on silica gel. 1H and 13C NMR spectra were recorded at 400 and 151 MHz in CDCl3 or DMSO-d6 using a BRUKER AVANCE III HD spectrometer. 1H and 13C chemical shifts are reported in parts per million relative to Me4Si using the residual solvent signal as an internal reference. Powder X-ray diffraction (PXRD) patterns were recorded on an X′Pert PRO SUPERA rotation anode X-ray diffractometer with Ni-filtered Cu Kα radiation (λ = 1.5418 Å). Elemental analyses (C, H, and N) were performed on a Carlo-Erbo CHNO-S microanalyzer. IR spectra (KBr disc) were recorded on a Nicolet MagNa-IR550 FT-IR spectrometer (4000−400 cm−1). High-resolution mass spectra (HRMS) were obtained with a GCT Premier (Micromass UK Limited) chemical ionization time-offlight mass spectrometer (CI-TOF). Experimental Procedures. Synthesis of 1g. To a MeCN (10 mL) solution of 4-phpymtH (30.2 mg, 0.16 mmol) and Et3N (400 mg, 4.0 mmol) was added a MeCN (10 mL) solution of CuI (14.3 mg, 0.075 mmol). The mixture was stirred for ∼1 h at ambient temperature to form a yellow precipitate. After filtration, the solid was washed with MeCN and diethyl ether and dried in air. Yield: 18 mg (90%). Anal. calcd for C64H48Cu6N14S6: C 48.44, H 3.05, N 12.36. Found: C 48.64, H 3.21, N 11.67%. IR: ν(CN, CC) 1629, 1578 cm−1. 1H NMR (400 MHz, CDCl3, ppm) δ 8.03 (d, J = 7.3 Hz, 2H), 7.51−7.38 (m, 5H). Synthesis of 1h. Orange solid of 1h was isolated in a similar manner to that used for the isolation of 1g using CuI (9.5 mg, 0.05 mmol) and 4,5-diphpymtH (26.4 mg, 0.10 mmol) as starting materials. Yield: 15.8 mg (92%). Anal. calcd for C100H78Cu6N14S6: C 58.61, H 3.84, N 9.57. Found: C 58.86, H 3.75, N 9.35%. IR: ν(CN, CC) 1629, 1556 cm−1. 1H NMR (400 MHz, CDCl3, ppm) δ 8.59 (s, 1H), 7.39 (d, J = 7.7 Hz, 2H), 7.33 (d, J = 2.9 Hz, 4H), 7.22 (d, J = 7.5 Hz, 2H), 7.17 (d, J = 3.7 Hz, 2H). Synthesis of 1i. A Pyrex glass tube (15 cm in length, 7 mm inner diameter) was loaded with CuI (9.5 mg, 0.05 mmol), 4,6-diphenyl-5,6dihydropyrimidine-2(1H)-thione (13.2 mg, 0.05 mmol), 2 mL of MeCN, and 0.1 mL of DMF. The tube was sealed and heated in an oven to 120 °C for 48 h and then cooled to ambient temperature at a rate of 5 °C per 60 min to give yellow crystals, which were collected by filtration, washed with MeCN and Et2O, and dried in vacuo. Yield: 15.5 mg (90%). Anal. calcd for C100H78Cu6N14S6: C 58.61, H 3.84, N 9.57. Found: C 59.06, H 3.63, N 9.39%. IR: ν(CN, CC) 1638, 1566 cm−1. 1H NMR (400 MHz, CDCl3, ppm) δ 8.08 (d, J = 6.9 Hz, 2H), 7.68 (d, J = 7.1 Hz, 2H), 7.52 (dd, J = 14.7, 7.3 Hz, 6H), 7.22 (s, 1H). X-ray Crystallography. Each single crystal (1g·2DMF·Et2O, 1h· 4CHCl3 and 1i) was mounted on a glass fiber with grease and cooled in a liquid nitrogen stream at 193 K (1g·2DMF·Et2O), 173 K (1h· 4CHCl3), or 293 K (1i). Crystallographic measurements were made on a Rigaku Saturn (1g·2DMF·Et2O and 1i) or a Bruker APEX-II 1211


Article

The Journal of Organic Chemistry 2-Methylpent-2-en-1-ol (3ah).15 Yield: 86 mg (86%). 1H NMR (600 MHz, CDCl3, ppm): δ 5.39 (t, J = 6.7 Hz, 1H), 3.98 (s, 2H), 2.03 (p, J = 7.4 Hz, 2H), 1.65 (s, 3H), 0.96 (t, J = 7.5 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 134.2, 128.3, 69.1, 21.0, 14.1, 13.6. HRMS m/z calcd for C6H12O [M + H]+ 101.0966, found 101.0967. 2-Furfurylalcohol (3ai).77 Yield: 74 mg (75%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.38 (s, 1H), 6.33 (s, 1H), 6.27 (s, 1H), 4.55 (s, 2H), 2.75−2.66 (m, 1H). 13C NMR (151 MHz, CDCl3, ppm): δ 154.0, 142.4, 110.3, 107.7, 57.2. HRMS m/z calcd for C5H6O2 [M + H]+ 99.0446, found 99.0448. Thiophen-2-ylmethanol (3aj).77 Yield: 84 mg (74%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.23 (s, 1H), 6.94 (s, 2H), 4.71 (s, 2H), 3.05−2.78 (m, 1H). 13C NMR (151 MHz, CDCl3, ppm): δ 144.0, 126.8, 125.5, 125.4, 59.7. HRMS m/z calcd for C5H6OS [M + H]+ 115.0217, found 115.0221. 3-Pyridylmethanol (3ak).77 Yield: 87 mg (80%). 1H NMR (400 MHz, CDCl3, ppm): δ 8.40 (s, 1H), 8.33 (s, 1H), 7.68 (d, J = 7.1 Hz, 1H), 7.24−7.19 (m, 1H), 5.16 (s, 1H), 4.63 (s, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 147.9, 147.8, 137.2, 135.2, 123.6, 61.8. HRMS m/z calcd for C6H7NO [M + H]+ 110.0606, found 110.0610. 4-Phenylbut-3-en-2-ol (3al).2 Yield: 138 mg (93%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.39 (d, J = 7.4 Hz, 2H), 7.33 (t, J = 7.3 Hz, 2H), 7.26 (t, J = 7.1 Hz, 1H), 6.57 (d, J = 16.0 Hz, 1H), 6.28 (dd, J = 15.9, 6.3 Hz, 1H), 4.53−4.46 (m, 1H), 2.30−2.16 (m, 1H), 1.39 (d, J = 6.4 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 136.7, 133.6, 129.3, 128.6, 127.6, 126.4, 68.8, 23.4. HRMS m/z calcd for C10H12O [M + H]+ 149.0966, found 149.0967. 1-(4-Styrylphenyl)ethan-1-ol (3am).99 Yield: 208 mg (93%). 1H NMR (400 MHz, DMSO-d6, ppm): δ 7.59 (d, J = 7.6 Hz, 2H), 7.55 (d, J = 7.9 Hz, 2H), 7.36 (dd, J = 15.7, 7.8 Hz, 4H), 7.30−7.20 (m, 3H), 5.16 (d, J = 4.1 Hz, 1H), 4.73 (dd, J = 10.8, 5.6 Hz, 1H), 1.32 (d, J = 6.4 Hz, 3H). 13C NMR (151 MHz, DMSO-d6, ppm): δ 147.4, 137.5, 135.8, 129.1, 128.7, 128.1, 127.9, 126.8, 126.6, 126.1, 68.3, 26.3. HRMS m/z calcd for C16H16O [M + H]+ 225.1279, found 225.1281. 1-Penten-3-ol (3an).47 Yield: 72 mg (84%). 1H NMR (400 MHz, CDCl3, ppm): δ 5.85 (ddd, J = 16.8, 10.2, 6.3 Hz, 1H), 5.22 (d, J = 17.2 Hz, 1H), 5.11 (d, J = 10.4 Hz, 1H), 4.02 (d, J = 5.8 Hz, 1H), 2.34−2.19 (m, 1H), 1.56 (dd, J = 8.1, 5.0 Hz, 2H), 0.92 (t, J = 7.4 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 140.9, 114.6, 74.4, 29.8, 9.5. HRMS m/z calcd for C5H10O [M + H]+ 87.0810, found 87.0814. Hex-5-en-2-ol (3ao).66 Yield: 82 mg (82%). 1H NMR (600 MHz, CDCl3, ppm): δ 5.83 (ddt, J = 16.9, 10.2, 6.7 Hz, 1H), 5.04 (ddd, J = 17.1, 3.4, 1.7 Hz, 1H), 4.96 (ddd, J = 10.1, 3.0, 1.2 Hz, 1H), 4.76 (s, 2H), 3.80 (dt, J = 12.4, 6.2 Hz, 1H), 2.53 (s, 1H), 2.18−2.09 (m, 2H), 1.19 (d, J = 6.2 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 138.4, 114.6, 67.4, 38.2, 30.0, 23.3. HRMS m/z calcd for C6H12O [M + H]+ 101.0966, found 101.0969. 6-Methylhept-5-en-2-ol (3ap).75 Yield: 105 mg (82%). 1H NMR (400 MHz, CDCl3, ppm): δ 5.13 (t, J = 6.6 Hz, 1H), 3.81 (dt, J = 12.3, 6.1 Hz, 1H), 2.07 (dt, J = 14.0, 6.8 Hz, 2H), 1.82 (s, 1H), 1.69 (s, 3H), 1.62 (s, 3H), 1.53−1.44 (m, 2H), 1.19 (d, J = 6.2 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 132.1, 124.2, 68.0, 39.3, 25.8, 24.6, 23.5, 17.7. HRMS m/z calcd for C8H16O [M + H]+ 129.1279, found 129.1281. 1,3-Diphenylprop-2-en-1-ol (3ba).2 Yield: 195 mg (93%). 1H NMR (400 MHz, DMSO-d6, ppm): δ 7.43 (d, J = 4.8 Hz, 4H), 7.37− 7.24 (m, 6H), 6.67 (d, J = 15.8 Hz, 1H), 6.42 (dd, J = 15.9, 6.3 Hz, 1H), 5.69 (d, J = 4.0 Hz, 1H), 5.31−5.27 (m, 1H). 13C NMR (151 MHz, DMSO-d6, ppm): δ 144.9, 137.1, 134.1, 129.0, 128.6, 128.5, 127.8, 127.3, 126.7, 126.6, 73.6. HRMS m/z calcd for C15H14O [M + H]+ 211.1123, found 211.1125. 3-(4-Chlorophenyl)-1-phenylprop-2-en-1-ol (3bb).2 Yield: 220 mg (90%). 1H NMR (600 MHz, DMSO-d6, ppm): δ 7.45 (d, J = 8.5 Hz, 2H), 7.42 (d, J = 7.4 Hz, 2H), 7.37−7.32 (m, 4H), 7.24 (t, J = 7.3 Hz, 1H), 6.65 (d, J = 15.8 Hz, 1H), 6.45 (dd, J = 15.9, 6.2 Hz, 1H), 5.70 (d, J = 4.2 Hz, 1H), 5.29−5.26 (m, 1H). 13C NMR (151 MHz, DMSO-d6, ppm): δ 144.2, 135.6, 134.6, 131.7, 128.5, 128.2, 128.0, 126.9, 126.8, 126.2, 73.1. HRMS m/z calcd for C15H13ClO [M + H]+ 245.0733, found 245.0735.

1-(Naphthalen-2-yl)-3-phenylprop-2-en-1-ol (3ca).78 Yield: 229 mg (88%). 1H NMR (600 MHz, DMSO-d6, ppm): δ 7.93−7.87 (m, 4H), 7.55 (dd, J = 8.5, 1.4 Hz, 1H), 7.51−7.46 (m, 2H), 7.44 (d, J = 7.4 Hz, 2H), 7.31 (t, J = 7.6 Hz, 2H), 7.22 (t, J = 7.3 Hz, 1H), 6.70 (d, J = 15.9 Hz, 1H), 6.48 (dd, J = 15.9, 6.3 Hz, 1H), 5.77 (d, J = 4.2 Hz, 1H), 5.44−5.41 (m, 1H). 13C NMR (151 MHz, DMSO-d6, ppm): δ 136.6, 133.4, 132.9, 132.2, 128.6, 128.3, 127.7, 127.7, 127.5, 129.4, 126.3, 126.0, 125.6, 125.0, 124.2, 73.2. HRMS m/z calcd for C19H16O [M + H]+ 261.1279, found 261.1282. 3-(4-Chlorophenyl)-1-phenylprop-2-en-1-ol (3cb).2 Yield: 222 mg (91%). 1H NMR (400 MHz, DMSO-d6, ppm): δ 7.47−7.38 (m, 6H), 7.31 (t, J = 7.4 Hz, 2H), 7.22 (t, J = 7.2 Hz, 1H), 6.66 (d, J = 15.8 Hz, 1H), 6.39 (dd, J = 15.8, 6.3 Hz, 1H), 5.79 (d, J = 4.0 Hz, 1H), 5.33− 5.26 (m, 1H). 13C NMR (151 MHz, DMSO-d6, ppm): δ 143.8, 136.9, 133.6, 131.8, 129.0, 129.0, 128.5, 128.5, 127.9, 126.8, 72.9. HRMS m/z calcd for C15H13ClO [M + H]+ 245.0733, found 245.0731. 3-(4-Nitrophenyl)-1-phenylprop-2-en-1-ol (3cc).100 Yield: 222 mg (87%). 1H NMR (600 MHz, CDCl3, ppm): δ 8.05 (d, J = 8.7 Hz, 2H), 7.49 (d, J = 8.7 Hz, 2H), 7.30 (d, J = 7.5 Hz, 2H), 7.25 (t, J = 7.5 Hz, 2H), 7.20 (dd, J = 9.3, 5.1 Hz, 1H), 6.63 (d, J = 15.8 Hz, 1H), 6.24 (dd, J = 15.8, 7.1 Hz, 1H), 5.40 (d, J = 7.0 Hz, 1H). 13C NMR (151 MHz, CDCl3, ppm): δ 150.0, 146.9, 135.8, 131.8, 130.0, 128.5, 128.1, 126.8, 126.5, 123.5, 74.0. HRMS m/z calcd for C15H13NO3 [M + H]+ 256.0974, found 256.0978. Transfer Hydrogenation of Unsaturated Carbonyls to Saturated Carbonyls. In a typical procedure, a test tube equipped with a magnetic stirring bar was charged with unsaturated carbonyl (0.5 mmol), K2CO3 (0.5 mmol), 1b (10 mol % Cu), and n-BuOH (2 mL). The reaction mixture was stirred at 120 °C for 24 h. After cooling to room temperature, the mixture was partitioned between water and ethyl acetate. The organic layer was separated, and the aqueous layer was extracted with ethyl acetate (3 × 15 mL). The combined organic layer was washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure. The crude product was purified by flash column chromatography. 1,3-Diphenylpropan-1-one (4ba).55 Yield: 193 mg (92%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.95 (d, J = 7.7 Hz, 2H), 7.55 (t, J = 7.2 Hz, 1H), 7.44 (t, J = 7.5 Hz, 2H), 7.28 (dt, J = 15.3, 7.6 Hz, 4H), 7.20 (t, J = 7.0 Hz, 1H), 3.30 (t, J = 7.7 Hz, 2H), 3.07 (t, J = 7.6 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 199.2, 141.3, 136.8, 133.0, 128.6, 128.5, 128.4, 128.0, 126.1, 40.4, 30.1. HRMS m/z calcd for C15H15O [M + H]+ 211.1123, found 211.1124. 3-(4-Chlorophenyl)-1-phenylpropan-1-one (4bb).55 Yield: 244 mg (92%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.88 (d, J = 8.3 Hz, 2H), 7.41 (d, J = 8.3 Hz, 2H), 7.30 (t, J = 7.4 Hz, 2H), 7.26−7.20 (m, 3H), 3.26 (t, J = 7.6 Hz, 2H), 3.06 (t, J = 7.6 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 197.8, 141.0, 139.5, 135.2, 129.4, 128.9, 128.6, 128.4, 126.2, 40.4, 30.0. HRMS m/z calcd for C15H14OCl [M + H]+ 245.0733, found 245.0728. 3-(4-Bromophenyl)-1-phenylpropan-1-one (4bc).55 Yield: 262 mg (91%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.80 (d, J = 8.2 Hz, 2H), 7.57 (d, J = 8.2 Hz, 2H), 7.29 (t, J = 7.3 Hz, 2H), 7.25−7.19 (m, 3H), 3.25 (t, J = 7.6 Hz, 2H), 3.05 (t, J = 7.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.1, 141.0, 135.5, 131.9, 129.5, 128.5, 128.4, 128.2, 126.2, 40.4, 30.0. HRMS m/z calcd for C15H14OBr [M + H]+ 289.0228, found 289.0233. 1-Phenyl-3-(4-(trifluoromethyl)phenyl)propan-1-one (4bd).55 Yield: 264 mg (95%). 1H NMR (600 MHz, CDCl3, ppm): δ 7.98− 7.92 (m, 2H), 7.56 (dd, J = 15.1, 7.7 Hz, 3H), 7.46 (t, J = 7.8 Hz, 2H), 7.37 (d, J = 8.0 Hz, 2H), 3.32 (t, J = 7.5 Hz, 2H), 3.13 (t, J = 7.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.5, 145.5, 136.7, 133.2, 128.8, 128.7, 128.0, 125.4, 125.2, 123.4, 39.8, 29.8. HRMS m/z calcd for C16H14OF3 [M + H]+ 279.0997, found 279.1005. 1-Phenyl-3-(p-tolyl)propan-1-one (4be).55 Yield: 208 mg (93%). 1 H NMR (400 MHz, CDCl3, ppm): δ 7.86 (d, J = 7.9 Hz, 2H), 7.25 (td, J = 15.9, 10.1 Hz, 7H), 3.27 (t, J = 7.7 Hz, 2H), 3.05 (t, J = 7.7 Hz, 2H), 2.40 (s, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.9, 143.8, 141.4, 134.4, 129.3, 128.5, 128.4, 128.2, 126.1, 40.3, 30.2, 21.6. HRMS m/z calcd for C16H17O [M + H]+ 225.1279, found 225.1275. 1212


Article

The Journal of Organic Chemistry 3-Mesityl-1-phenylpropan-1-one (4bf).101 Yield: 207 mg (82%). H NMR (400 MHz, CDCl3, ppm): δ 7.96 (d, J = 7.7 Hz, 2H), 7.56 (t, J = 7.2 Hz, 1H), 7.46 (t, J = 7.5 Hz, 2H), 6.87 (s, 2H), 3.15−3.08 (m, 2H), 3.07−2.99 (m, 2H), 2.31 (s, 6H), 2.27 (s, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 199.6, 136.8, 136.1, 135.5, 134.8, 133.1, 129.1, 128.6, 128.0, 37.9, 23.7, 20.8, 19.7. HRMS m/z calcd for C18H21O [M + H]+ 253.1592, found 253.1589. 3-(Benzo[d][1,3]dioxol-5-yl)-1-phenylpropan-1-one (4bg).102 Yield: 221 mg (87%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.95 (d, J = 7.7 Hz, 2H), 7.55 (t, J = 7.3 Hz, 1H), 7.44 (t, J = 7.6 Hz, 2H), 6.71 (dd, J = 16.1, 7.6 Hz, 3H), 5.90 (s, 2H), 3.25 (t, J = 7.6 Hz, 2H), 2.98 (t, J = 7.6 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 199.1, 147.6, 145.8, 136.8, 135.0, 133.0, 128.6, 128.0, 121.1, 108.9, 108.2, 100.8, 40.6, 29.8. HRMS m/z calcd for C16H15O3 [M + H]+ 255.1021, found 255.1023. 1-Phenyl-3-(pyridin-3-yl)propan-1-one (4bh).103 Yield: 152 mg (72%). 1H NMR (400 MHz, CDCl3, ppm): δ 8.54 (s, 1H), 8.46 (d, J = 4.0 Hz, 1H), 7.95 (d, J = 7.6 Hz, 2H), 7.58 (dd, J = 16.1, 7.7 Hz, 2H), 7.47 (d, J = 7.6 Hz, 2H), 7.23 (dd, J = 7.4, 5.0 Hz, 1H), 3.33 (t, J = 7.4 Hz, 2H), 3.09 (t, J = 7.4 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.4, 149.8, 147.5, 136.7, 136.6, 136.2, 133.3, 128.7, 128.0, 123.4, 39.7, 27.1. HRMS m/z calcd for C14H14NO [M + H]+ 212.1075, found 212.1080. 1-(Naphthalen-2-yl)-3-phenylpropan-1-one (4ca).55 Yield: 237 mg (91%). 1H NMR (400 MHz, CDCl3, ppm): δ 8.44 (s, 1H), 8.03 (d, J = 8.4 Hz, 1H), 7.92 (d, J = 7.8 Hz, 1H), 7.86 (t, J = 7.7 Hz, 2H), 7.55 (dd, J = 13.0, 7.7 Hz, 2H), 7.29 (s, 4H), 7.22 (d, J = 6.8 Hz, 1H), 3.43 (t, J = 7.5 Hz, 2H), 3.12 (t, J = 6.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 199.1, 141.3, 135.6, 134.2, 132.5, 129.7, 129.5, 128.5, 128.4, 128.4, 127.7, 126.7, 126.1, 123.8, 40.5, 30.3. HRMS m/z calcd for C19H17O [M + H]+ 261.1279, found 261.1281. 1-(4-Chlorophenyl)-3-phenylpropan-1-one (4cb).55 Yield: 229 mg (94%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.94 (d, J = 7.7 Hz, 2H), 7.54 (t, J = 7.3 Hz, 1H), 7.44 (t, J = 7.6 Hz, 2H), 7.24 (d, J = 8.1 Hz, 2H), 7.17 (d, J = 8.1 Hz, 2H), 3.26 (t, J = 7.5 Hz, 2H), 3.03 (t, J = 7.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.8, 139.7, 136.7, 133.1, 131.8, 129.8, 128.6, 128.6, 128.0, 40.1, 29.3. HRMS m/z calcd for C15H14OCl [M + H]+ 245.0733, found 245.0727. 1-(4-Bromophenyl)-3-phenylpropan-1-one (4cc).55 Yield: 259 mg (90%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.94 (d, J = 7.6 Hz, 2H), 7.55 (t, J = 7.3 Hz, 1H), 7.45 (t, J = 7.6 Hz, 2H), 7.40 (d, J = 8.1 Hz, 2H), 7.12 (d, J = 8.1 Hz, 2H), 3.27 (t, J = 7.5 Hz, 2H), 3.02 (t, J = 7.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.7, 140.2, 136.7, 133.1, 131.5, 130.2, 128.6, 128.0, 119.9, 40.0, 29.4. HRMS m/z calcd for C15H14OBr [M + H]+ 289.0228, found 289.0215. 3-Phenyl-1-(p-tolyl)propan-1-one (4 cd).55 Yield: 208 mg (93%). 1 H NMR (400 MHz, CDCl3, ppm): δ 7.95 (d, J = 7.6 Hz, 2H), 7.54 (t, J = 7.3 Hz, 1H), 7.44 (t, J = 7.6 Hz, 2H), 7.13 (q, J = 7.9 Hz, 4H), 3.27 (t, J = 7.7 Hz, 2H), 3.03 (t, J = 7.7 Hz, 2H), 2.32 (s, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 199.3, 138.2, 136.9, 135.6, 133.0, 129.2, 128.6, 128.3, 128.0, 40.6, 29.7, 21.0. HRMS m/z calcd for C16H17O [M + H]+ 225.1279, found 225.1284. 1-(4-Methoxyphenyl)-3-phenylpropan-1-one (4ce).55 Yield: 221 mg (92%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.95 (d, J = 7.7 Hz, 2H), 7.55 (t, J = 7.3 Hz, 1H), 7.45 (t, J = 7.5 Hz, 2H), 7.17 (d, J = 8.3 Hz, 2H), 6.84 (d, J = 8.3 Hz, 2H), 3.78 (s, 3H), 3.27 (t, J = 7.6 Hz, 2H), 3.01 (t, J = 7.6 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 199.4, 158.0, 136.9, 133.3, 133.0, 129.3, 128.6, 128.0, 113.9, 55.3, 40.7, 29.3. HRMS m/z calcd for C16H17O2 [M + H]+ 241.1229, found 241.1224. 1-(2-Methoxyphenyl)-3-phenylpropan-1-one (4cf).104 Yield: 192 mg (80%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.98 (d, J = 7.7 Hz, 2H), 7.54 (t, J = 7.2 Hz, 1H), 7.44 (t, J = 7.5 Hz, 2H), 7.20 (d, J = 6.2 Hz, 2H), 6.95−6.77 (m, 2H), 3.82 (s, 3H), 3.32−3.23 (m, 2H), 3.09− 3.01 (m, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 200.0, 157.5, 137.0, 132.9, 130.1, 129.5, 128.5, 128.1, 127.5, 120.5, 110.2, 55.2, 38.9, 25.7. HRMS m/z calcd for C16H17O2 [M + H]+ 241.1229, found 241.1223. 1-(3-Methoxyphenyl)-3-phenylpropan-1-one (4cg).105 Yield: 199 mg (83%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.96 (d, J = 7.6 Hz,

2H), 7.55 (t, J = 7.3 Hz, 1H), 7.45 (t, J = 7.5 Hz, 2H), 7.22 (t, J = 7.8 Hz, 1H), 6.85 (d, J = 7.5 Hz, 1H), 6.80 (s, 1H), 6.76 (d, J = 8.2 Hz, 1H), 3.79 (s, 3H), 3.30 (t, J = 7.7 Hz, 2H), 3.05 (t, J = 7.7 Hz, 2H). 13 C NMR (151 MHz, CDCl3, ppm): δ 199.2, 159.7, 142.9, 136.8, 133.1, 129.5, 128.6, 128.0, 120.8, 114.2, 111.4, 55.2, 40.4, 30.2. HRMS m/z calcd for C16H17O2 [M + H]+ 241.1229, found 241.1237. 3-Phenyl-1-(thiophen-2-yl)propan-1-one (4ch).55 Yield: 153 mg (71%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.67 (d, J = 3.4 Hz, 1H), 7.59 (d, J = 4.8 Hz, 1H), 7.32−7.26 (m, 2H), 7.24 (d, J = 7.0 Hz, 2H), 7.20 (d, J = 7.3 Hz, 1H), 7.09 (t, J = 4.2 Hz, 1H), 3.22 (t, J = 7.7 Hz, 2H), 3.06 (t, J = 7.6 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 192.0, 144.0, 140.9, 133.5, 131.7, 128.4, 128.3, 128.0, 126.1, 41.0, 30.3. HRMS m/z calcd for C13H13OS [M + H]+ 217.0687, found 217.0678. 3-Phenyl-1-(pyridin-3-yl)propan-1-one (4ci).105 Yield: 165 mg (78%). 1H NMR (400 MHz, CDCl3, ppm): δ 9.15 (s, 1H), 8.75 (d, J = 4.2 Hz, 1H), 8.20 (d, J = 7.9 Hz, 1H), 7.39 (dd, J = 7.7, 4.9 Hz, 1H), 7.32−7.27 (m, 2H), 7.26−7.17 (m, 3H), 3.31 (t, J = 7.5 Hz, 2H), 3.08 (t, J = 7.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 198.0, 153.4, 149.5, 140.7, 135.3, 132.0, 128.6, 128.4, 126.3, 123.6, 40.6, 29.8. HRMS m/z calcd for C14H14NO [M + H]+ 212.1075, found 212.1068. 1-Phenyldecan-1-one (4cj).105 Yield: 172 mg (74%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.96 (d, J = 7.5 Hz, 2H), 7.54 (t, J = 7.1 Hz, 1H), 7.45 (t, J = 7.4 Hz, 2H), 2.95 (t, J = 7.3 Hz, 2H), 1.84−1.64 (m, 2H), 1.30 (d, J = 29.3 Hz, 12H), 0.88 (t, J = 5.9 Hz, 3H). 13C NMR (151 MHz, CDCl3, ppm): δ 137.1, 132.8, 128.5, 128.0, 38.6, 31.9, 29.5, 29.4, 29.3, 24.4, 22.6, 14.1. HRMS m/z calcd for C16H25O [M + H]+ 233.1905, found 233.1901. 2-Benzylcyclohexan-1-one (4ck).106 Yield: 152 mg (81%). 1H NMR (600 MHz, CDCl3, ppm): δ 7.26 (t, J = 7.6 Hz, 2H), 7.18 (t, J = 7.4 Hz, 1H), 7.15 (d, J = 7.5 Hz, 2H), 3.23 (dd, J = 14.0, 4.8 Hz, 1H), 2.58−2.51 (m, 1H), 2.45−2.38 (m, 2H), 2.36−2.28 (m, 1H), 2.03 (dddt, J = 23.3, 11.6, 6.0, 3.1 Hz, 2H), 1.85−1.79 (m, 1H), 1.66 (ddd, J = 16.6, 8.3, 3.8 Hz, 1H), 1.57 (qt, J = 13.1, 3.6 Hz, 1H), 1.35 (qd, J = 12.5, 3.6 Hz, 1H). 13C NMR (151 MHz, CDCl3, ppm): δ 212.7, 140.5, 129.3, 128.5, 126.1, 52.7, 42.3, 35.6, 33.6, 28.8, 25.5. HRMS m/z calcd for C13H17O [M + H]+ 189.1279, found 189.1284. 3-Phenylpropanal (4aa).25 Yield: 68 mg (51%). 1H NMR (400 MHz, CDCl3, ppm): δ 9.77 (s, 1H), 7.27 (t, J = 7.3 Hz, 2H), 7.18 (t, J = 7.7 Hz, 3H), 2.93 (t, J = 7.5 Hz, 2H), 2.73 (t, J = 7.5 Hz, 2H). 13C NMR (151 MHz, CDCl3, ppm): δ 201.6, 140.5, 128.6, 128.4, 126.4, 45.3, 28.2. HRMS m/z calcd for C9H10O [M + H]+ 135.0778, found 135.0776.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b02676. 1 H NMR and 13C NMR spectra of 1g−1i, products, PXRD patterns of 1g−1i, and computational details (PDF) X-ray crystallographic data (CIF) Accession Codes

CCDC 1522340−1522342 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: + 44 1223 336033.

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*E-mail: [email protected]. Phone: 86-512-65883569. *E-mail: [email protected]. *E-mail: [email protected]. Fax: 86-512-65880328. Phone: 86-512-65882865. ORCID

Jian-Ping Lang: 0000-0003-2942-7385 1213


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M.J.Z. and D.W.T. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (Grants 21771131, 21471108, 21531006, 21101109, and 21773163), the Natural Science Foundation of Jiangsu Province (Grant BK20161276), the State Key Laboratory of Organometallic Chemistry of Shanghai Institute of Organic Chemistry (Grant 2018kf05), the Priority Academic Program Development of Jiangsu Higher Education Institutions, the Natural Science Foundation of the Jiangsu Higher Education Institutions (Grant 16KJD150001), and the “SooChow Scholar” Program of Soochow University. We are grateful for the useful comments of the editor and reviewers.

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