Burgess Reagent Facilitated Alcohol Oxidations in DMSO - The

Dec 30, 2016 - Herein we show that, in the presence of dimethyl sulfoxide, the Burgess reagent efficiently and rapidly facilitates the oxidation of a ...
0 downloads 0 Views 599KB Size
Download PDF
Article pubs.acs.org/joc

Burgess Reagent Facilitated Alcohol Oxidations in DMSO Prakash R. Sultane† and Christopher W. Bielawski*,†,‡ †

Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea Department of Chemistry and Department of Energy Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea

‡

S Supporting Information *

ABSTRACT: The Burgess reagent ([methoxycarbonylsulfamoyl]triethylammonium hydroxide) has historically found utility as a dehydrating agent. Herein we show that, in the presence of dimethyl sulfoxide, the Burgess reagent efficiently and rapidly facilitates the oxidation of a broad range of primary and secondary alcohols to their corresponding aldehydes and ketones in excellent yields and under mild conditions, and can be combined with other transformations (e.g., Wittig olefinations). A mechanism similar to those described for the Pfitzner−Moffatt and Swern oxidations is proposed.

■

INTRODUCTION In 1968, Atkins and Burgess reported the synthesis of the inner salt [methoxycarbonylsulfamoyl]triethylammonium hydroxide (1) and described its utility in facilitating alcohol dehydrations.1 Subsequently, the aforementioned compound, which is now colloquially referred to as the “Burgess reagent”, has been successfully employed as a selective and mild dehydrating agent for a broad range of secondary (e.g., see Figure 1) and tertiary

its use in late stage transformations found in the total syntheses of numerous natural products.8 The Burgess reagent has also been used to convert 1,2-diols into 1,2-amino alcohols and has facilitated the synthesis of α- and β-glycosylamines.9 Several reviews that highlight the utility of 1 as well as its derivatives6,7 are currently available.10 At nearly the same time that the Burgess reagent was introduced, Parikh and Doering reported11 (1967) that the sulfur trioxide pyridine complex (C5H5N·SO3) activates dimethyl sulfoxide (DMSO) in the presence of a base (e.g., Et3N) and facilitates the oxidation of primary and secondary alcohols. While the Parikh−Doering oxidation reaction operates under mild conditions, relatively large excesses (3−6 equiv) of pure C5H5N·SO3 are required and, as a result, other activated DMSO-mediated oxidations are often favored.12 We hypothesized that 1, which upon the liberation of triethylamine, should generate an electrophilic dioxosulfimidinum species that may activate DMSO and facilitate oxidation reactions. Herein we report that the Burgess reagent may be used to oxidize primary and secondary alcohols to their respective aldehydes and ketones in the presence of DMSO.13 The reaction is rapid (minutes), operates under mild conditions (room temperature), and affords high yields of products from a broad range of functionally diverse starting materials.

■

RESULTS AND DISCUSSION In an initial experiment, benzyl alcohol ([BnOH]0 = 0.5 M) was treated with 2 equiv of 1 in anhydrous DMSO at room temperature (Scheme 1).14 After 5 min, 1H NMR spectroscopic analysis of the crude reaction mixture indicated that benzaldehyde (3a) was formed in quantitative yield along with dimethyl sulfide. Subsequent efforts were directed toward optimizing the reaction. After dissolving benzyl alcohol

Figure 1. Various uses of the Burgess reagent (1).

alcohols1 as well as a reagent for converting primary alcohols, primary amides, formamides, and primary nitroalkanes into their respective urethanes,1 nitriles,2 isocyanides,3 and nitrile oxides.4 The compound has also been employed in cyclodehydrations,5 which have been particularly useful in peptide modification chemistry, and for the preparation of sulfamides6 and cyclic sulfamidates7a from their corresponding amines and epoxides. The mild and selective nature of 1 is underscored by © XXXX American Chemical Society

Received: October 31, 2016

A

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry Scheme 3. Oxidation of Secondary Alcoholsa

Scheme 1. Oxidation of Benzyl Alcohol to Benzaldehyde

([BnOH]0 = 0.5 M) in anhydrous DMSO at room temperature, 1 equiv of the Burgess reagent was added to the solution. Analysis of the crude reaction mixture using 1H NMR spectroscopy revealed that the benzyl alcohol was completely consumed within 5 min; benzaldehyde was subsequently isolated in 94% yield. Likewise, 80% of 1-phenylethanol was converted to acetophenone within 5 min upon treatment with 1 equiv of 1 under the aforementioned conditions and quantitative formation of the ketone was observed when 1.3 equiv of 1 was used. The formation of mixed thioacetals12 (e.g., 4), a common side product found in activated DMSO-based oxidations, or urethanes1 were not observed. Based on the aforementioned results, we concluded that 1.3 equiv of the Burgess reagent with respect to the alcohol substrate was sufficient and practical. As summarized in Schemes 2 and 3, a broad range of primary and secondary alcohols were successfully oxidized and their corresponding aldehydes and ketone products in high isolated yields. Overoxidation of the aldehydes to the corresponding carboxylic acids was not observed. Likewise, olefinic products were not

a

Isolated yields are shown in parentheses. All reactions were performed using 1 mmol of alcohol and 1.3 mmol of the Burgess reagent in anhydrous DMSO (2 mL) at room temperature for 5 min. b Isolated as its 2,4-dinitrophenylhydrazone derivative.

detected when secondary alcohols containing α-hydrogens were subjected to the reaction conditions. The reaction also appeared to show good tolerance to functional groups as substrates containing carboxylic acids, esters, aryl ethers, or amides were successfully oxidized. Finally, the mild and selective nature of the transformation was probed with NCbz-(S)-phenylalaninol (CBz = carboxybenzyl); the corresponding aldehyde 3o was obtained in excellent yield and without epimerization.15 To gain a deeper understanding of the oxidation reaction, a series of control experiments were performed. When benzyl alcohol was treated with the Burgess reagent (1.3 equiv) and excess diphenylsulfoxide, a disubsituted sulfoxide devoid of αhydrogens, in CH2Cl2 the formation of benzaldehyde was not detected. Likewise, no reaction was observed by 1H NMR spectroscopy when trityl alcohol was introduced to the Burgess reagent in the presence of DMSO.16 As derivatives of the Burgess reagent are known,6,7 a series containing different amines were prepared (see Figure 2) and

Scheme 2. Oxidation of Primary Alcoholsa

Figure 2. Structures of modified Burgess reagents.

explored for their abilities to facilitate the oxidations of alcohols. Under otherwise identical conditions to those described above, no reaction was observed when benzyl alcohol was treated with 6a, even after extended periods of time (up to 12 h). However, at elevated temperatures (60 °C), benzaldehyde (3a) and thioacetal 4 were formed in 93% and 7% yield, respectively, as determined by 1H NMR spectroscopy. Similarly, no reaction was observed when benzyl alcohol was treated with 6b at room temperature, even after 12 h, although small quantities of the

a

Isolated yields are shown in parentheses. All reactions were performed using 1 mmol of alcohol and 1.3 mmol of the Burgess reagent in anhydrous DMSO (2 mL) at room temperature for 5 min. b Isolated as its 2,4-dinitrophenylhydrazone derivative. B

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry Scheme 5. Summary of Competition Experimentsa

aldehyde product (10% conversion) were observed at 60 °C. The most effective derivative tested was 6c, which was found to convert 88% of the starting material to the expected product at room temperature. Collectively, these results indicated that the use of Burgess-type reagents containing relatively basic amines are needed to facilitate alcohol oxidations in DMSO. Next, the versatility of the aforementioned methodology was probed by combining Burgess reagent-facilitated oxidations with Wittig olefinations to access γ-amino esters in a single pot. When N-Boc-(S)-valinol (Boc = tert-butyloxycarbonyl) (1 mmol) was treated with 1 (1.3 mmol) in DMSO (4 mL) followed by the addition of the Wittig reagent 7d (1.5 mmol), the corresponding unsaturated ester 7a was isolated in good yield (78%) and without racemization (Scheme 4).17 The reaction conditions were found to tolerate CBz protecting groups as well (c.f., 7b and 7c). Scheme 4. One Pot Alcohol Oxidation/Wittig Olefination Approach to γ-Amino Estersa

a

All reactions were performed using 0.1 mmol of each alcohol and 0.13 mmol of the Burgess reagent in DMSO-d6 (0.6 mL) at room temperature for 5 min. Conversions were determined by 1H NMR spectroscopy

Scheme 6. Proposed Mechanism for the Oxidation of Alcohols Using the Burgess Reagent in DMSO

a

Isolated yields are shown in parentheses. All reactions were performed using 1 mmol of alcohol, 1.3 mmol of the Burgess reagent and 1.5 mmol of the Wittig reagent in anhydrous DMSO (4 mL) at room temperature for 3 h.

To elucidate of the oxidation mechanism, the kinetics of various alcohol oxidation reactions were evaluated using 1H NMR spectroscopy. The conversions of benzyl alcohol (kinit = 2.4 × 10−2 mM−1 s−1), 4-methoxyphenylmethanol (kinit = 3.4 × 10−2 mM−1 s−1), 4-trifluorophenylmethanol (kinit = 1.8 × 10−2 mM−1 s−1), and benzyl alcohol-α,α-d2 (kinit = 2.2 × 10−2 mM−1 s−1) to their respective products were independently monitored over time (conditions: [alcohol]0 = 35 mM, [1]0 = 46.2 mM, [1,3,5-trimethoxybenzene (internal standard)]0 = 35 mM, DMSO-d6, 21 °C). Collectively, the kinetic studies revealed that electron rich alcohols react faster than their electron deficient congeners, at least during the early stages of the reaction. Moreover, the initial rate constant measured for the oxidation of benzyl alcohol was nearly the same as its deuterated analogue, which excluded cleavage of the C− H(D) bond as the rate-determining step. To verify the kinetics data, series of competition experiments were performed. As summarized in Scheme 5, electron rich alcohols afforded higher conversions to their corresponding products when compared to their electron deficient analogues. Likewise, subjecting an equimolar mixture of benzyl alcohol and a deuterated analogue to the Burgess reagent afforded the respective benzaldehyde products in nearly a 1:1 ratio. Collectively, the data suggested to us that the rate-determining step involved nucleophilic attack of the alcohol on an activated substrate. Based on the aforementioned results, an oxidation mechanism was deduced and is proposed in Scheme 6. The reaction may start with the attack of DMSO on the Burgess reagent to afford sulfonium ion 8. Benzyl alcohol may then

react with 8 to form an alkoxysulfonium intermediate (9), which subsequently undergoes deprotonation. Decomposition of the resulting ylide (10) should afford the carbonyl containing compound as well as dimethyl sulfide, which was observed by 1 H NMR spectroscopy (vide supra).18 Overall, the oxidation mechanism is similar to those described for the Pfitzner−Moffatt19 and Swern oxidations although it may proceed with a different rate-determining step. For example, the rate-determining step of the Swern oxidation has been reported to be deprotonation of the alkoxysulfonium intermediate to form the corresponding ylide.12 As a result, the Swern and related oxidations typically involve a series of timed reagent additions and are conducted at low temperatures (−78 °C). In comparison, the methodology described herein can be performed in one pot as all requisite activation agents are generated in situ and conducted at room temperature. In conclusion, we have discovered that the Burgess reagent, a compound that has historically found utility as a dehydrating agent, may be used to oxidize primary and secondary alcohols to their corresponding aldehydes and ketones in dimethyl sulfoxide. The reactions were found to be rapid, operated under mild conditions, and afforded oxidized products in excellent isolated yields. The methodology is advantageous to others in that it is convenient and broadly useful, the oxidation reaction C

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry

complete (∼1 h), the triethylammonium hydrochloride precipitate was removed by filtration, and the filtrate was concentrated to give 1 as an off-white solid (21.7 g, 86% yield). mp 71−73 °C; IR (ATR): νco 1686, 1440, 1327, 1245, 1108; 1H NMR (400 MHz, CDCl3): δ 3.69 (s, 3H), 3.47 (q, J = 7.3 Hz, 6H), 1.41 (t, J = 7.3 Hz, 9H); 13C NMR (100 MHz, CDCl3): δ 158.4, 53.4, 50.6, 9.5; HRMS (ESI): m/z calcd for C8H18N2O4SNa [M+Na]+, 261.0879; found, 261.0849. Benzaldehyde (3a).20 Using Procedure A afforded 0.1 g (94% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 10.02 (s, 1H), 7.89−7.87 (m, 2H), 7.65−7.61 (m, 1H), 7.55−7.51 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 192.5, 136.5, 134.6, 129.9, 129.1; GCMS (EI): m/z 106. 4-Methoxybenzaldehyde (3b).21 Using Procedure A afforded 0.13 g (94% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 9.87 (s, 1H), 7.82 (d, J = 8.8 Hz, 2H), 6.99 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 190.1, 164.7, 132.1, 130.1, 114.4, 55.7; GCMS (EI): m/z 136. 4-Trifluoromethylbenzaldehyde (3c).22 Using Procedure A afforded 0.15 g (89% yield) of the desired product as a colorless liquid. 1 H NMR (400 MHz, CDCl3): δ 10.11 (s, 1H), 8.0 (d, J = 8.0 Hz, 2H), 7.80 (d, J = 8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 191.3, 138.9, 135.7 (q, J = 32.7 Hz), 130.1, 126.2 (q, J = 3.8 Hz), 123.6 (q, J = 272.9 Hz); GCMS (EI): m/z 174. 4-Nitrobenzaldehyde (3d).22 Using Procedure B afforded 0.142 g (94% yield) of the desired product as a light yellow solid. 1H NMR (400 MHz, CDCl3): δ 10.16 (s, 1H), 8.40 (d, J = 8.7 Hz, 2H), 8.08 (d, J = 8.7 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 190.4, 151.3, 140.2, 130.6, 124.5; GCMS (EI): m/z 151. 4-Formylbenzoic Acid (3e).23 A 25 mL Schlenk flask outfitted with a septum was charged with the corresponding alcohol (1 mmol), anhydrous DMSO (2 mL), and a stir bar. To the resulting solution was added freshly prepared Burgess reagent (1.3 mmol). After stirring at ambient temperature for 5 min, the reaction mixture was quenched by the addition of 1 N HCl (aq.). The mixture was then diluted with diethyl ether and water. The organic layer was isolated and the aqueous layer was washed twice with diethyl ether. The combined organic layers were washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure. Purification of the residue by silica gel column chromatography (n-pentane:Et2O, 7:3 v/v) afforded 0.14 g (92%) of the desired product as an off-white solid. 1H NMR (400 MHz, DMSO-d6): δ 10.10 (s, 1H), 8.13 (d, J = 8.2 Hz, 2H), 8.01 (d, J = 8.2 Hz, 2H); 13C NMR (100 MHz, DMSO-d6): δ 193.1, 166.6, 138.8, 136.0, 129.9, 129.6; MS (ESI) [M−H]+: m/z 149. Methyl 4-Formylbenzoate (3f).24 Using Procedure B afforded 0.15 g (94% yield) of the desired product as an off-white solid. 1H NMR (400 MHz, CDCl3): δ 10.10 (s, 1H), 8.20 (d, J = 8.3 Hz, 2H), 7.95 (d, J = 8.5 Hz, 2H), 3.96 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 191.8, 166.2, 139.3, 135.2, 130.3, 129.7, 52.7; MS (ESI) [M+H]+: m/z 165. N-Benzyl-4-formylbenzamide (3g).25 Using Procedure B afforded 0.15 g (92% yield) of the desired product as an off-white solid. 1H NMR (400 MHz, CDCl3): δ 10.08 (s, 1H), 7.95 (s, 4H), 7.39−7.31 (m, 5H), 6.43 (bs, 1H), 4.66 (d, J = 5.6 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 191.6, 166.4, 139.7, 138.4, 137.8, 130.0, 129.0, 128.2, 128.0, 127.8, 44.5; MS (ESI) [M+H]+: m/z 240. Picolinaldehyde (3h).26 Using Procedure A afforded 95 mg (88% yield) of the desired product as a pale yellow liquid. 1H NMR (400 MHz, CDCl3): δ 10.06 (s, 1H), 8.77 (d, J = 4.7 Hz, 1H), 7.94 (d, J = 7.7 Hz, 1H), 7.86 (t, J = 7.6 Hz, 1H), 7.60−7.41 (m, 1H); 13C NMR (100 MHz, CDCl3): δ 193.5, 153, 150.3, 137.2, 128, 121.8; GCMS (EI): m/z 107. Cinnamaldehyde (3i).21 Using Procedure A afforded 0.12 g (91% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 9.72 (d, J = 7.7 Hz, 1H), 7.63−7.54 (m, 2H), 7.49 (d, J = 15.9 Hz, 1H), 7.46−7.43 (m, 3H), 6.73 (dd, J = 15.9, 7.7 Hz, 1H); 13C NMR (100 MHz, CDCl3): δ 193.9, 153.0, 134.2, 131.4, 129.23, 128.8, 128.6; GCMS (EI): m/z 132. 3-Phenylpropiolaldehyde (3j).27 Using Procedure A afforded 0.116 g (89% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 9.43 (s, 1H), 7.97−7.56 (m, 2H), 7.56−7.46

does not evolve toxic byproducts (e.g., carbon monoxide), low temperatures or timed additions are not required, and the oxidation agent is commercially available.

■

EXPERIMENTAL SECTION

General Considerations. Unless otherwise specified, all reagents were purchased from commercial sources and used without further purification. Solvents were dried and degassed using a solvent purification system. Aluminum-backed plates precoated with silica gel 60F254 were used for thin layer chromatography and were visualized with a UV lamp or by staining with 2,4-dinitrophenylhydrazine. 1H NMR and 13C NMR spectra were recorded in CDCl3 (internal standard: 7.26 ppm, 1H; 77.2 ppm, 13C), CD2Cl2 (internal standard: 5.32 ppm, 1H; 54.0 ppm, 13C), acetone-d6 (internal standard: 2.05 ppm, 1H; 29.8 ppm, 13C), or DMSO (internal standard: 2.5 ppm, 1 H; 39.5 ppm, 13C) using 400 and 100 MHz spectrometers, respectively. Coupling constants (J) are expressed in hertz (Hz). Gas chromatograph mass spectrometry data were obtained with a GCMS spectrometer. High-resolution mass spectrometry (HRMS) data were obtained on a time-of-flight instrument. Optical rotations were determined using a polarimeter. Melting points are uncorrected. General Procedures. Procedure A. A 25 mL Schlenk flask outfitted with a septum was charged with an alcohol (1 mmol), anhydrous DMSO (2 mL), and a stir bar. To the resulting solution was added freshly prepared Burgess reagent (1.3 mmol). After stirring the resulting mixture at ambient temperature for 5 min, the reaction mixture was diluted with diethyl ether and water. The organic layer of the mixture was isolated and the aqueous layer was washed twice with diethyl ether. The combined organic layers were washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (n-pentane: Et2O, 9:1 v/v). Procedure B. A 25 mL Schlenk flask outfitted with a septum was charged with an alcohol (1 mmol), anhydrous DMSO (2 mL), and a stir bar. To the resulting solution was added freshly prepared Burgess reagent (1.3 mmol). After 5 min, the resulting mixture was poured onto ice. The precipitate was filtered, washed with cold water, and dried under reduced pressure to afford pure product. Procedure C. A 25 mL Schlenk flask outfitted with a septum was charged with an alcohol (1 mmol), anhydrous DMSO (2 mL), and a stir bar. To the resulting solution was added freshly prepared Burgess reagent (1.3 mmol). After stirring at ambient temperature for 5 min, the reaction mixture was diluted with ethanol and H2O. Next, 2,4dinitrophenyl hydrazine (1.05 mmol) was added followed by conc. H2SO4 (0.2 mL) and the resulting reaction mixture was stirred for another 10 min. Formation of the hydrazone was indicated by appearance of an orange precipitate, which was filtered, washed with cold water, collected, and dried under reduced pressure. Procedure D. A 25 mL Schlenk flask outfitted with a septum was charged with an alcohol (1 mmol), anhydrous DMSO (4 mL), and a stir bar. To the resulting solution was added freshly prepared Burgess reagent (1.3 mmol) followed by a Wittig salt (1.5 mmol). After stirring the resulting mixture at ambient temperature for 3 h, the reaction mixture was diluted with diethyl ether and water. The organic layer of the mixture was isolated and the aqueous layer was washed twice with diethyl ether. The combined organic layers were washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (n-hexane:EtOAc, 9:1 v/v). The Burgess Reagent (1). Following procedures reported in the literature,1d−f a solution of chlorosulfonylisocyanate (9.23 mL, 106 mmol) in benzene (50 mL) at 0 °C was added to a solution of methanol (4.5 mL, 111.3 mmol) in benzene (20 mL) over the course of 30 min. Once the addition was complete, the residual solvent was removed from the reaction mixture under reduced pressure to give the desired sulfamoyl chloride intermediate as a white solid. A solution of the newly formed sulfamoyl chloride in a benzene:toluene mixture (50 mL:50 mL) was added dropwise to a solution of Et3N (33.2 mL, 238.5 mmol) in benzene (150 mL) at 25 °C. After the addition was D

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry (m, 1H), 7.45−7.36 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 176.9, 133.4, 131.4, 128.9, 119.6, 95.3, 88.6; GCMS (EI): m/z 130. 6-Bromohexanal (3k).28 Using Procedure A afforded 0.15 g (88% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 9.78 (t, J = 1.6 Hz, 1H), 3.41 (t, J = 6.7 Hz, 2H), 2.47 (td, J = 7.2, 1.6 Hz, 2H), 1.93−1.82 (m, 2H), 1.71−1.61 (m, 2H), 1.53−1.43 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 202.3, 43.8, 33.5, 32.6, 27.8, 21.3; GCMS (EI): m/z 178. (E)-1-(2,4-Dinitrophenyl)-2-(3-methylbutylidene)hydrazine (3l).29 Using Procedure C afforded 0.23 g (86% yield) of the desired product as an orange solid. 1H NMR (400 MHz, CDCl3): δ 11.03 (s, 1H), 9.12 (d, J = 2.6 Hz, 1H), 8.30 (ddd, J = 9.6, 2.6, 0.8 Hz, 1H), 7.94 (d, J = 9.6 Hz, 1H), 7.53 (t, J = 5.8, 1H), 2.32 (dd, J = 6.9, 5.8 Hz, 2H), 1.98 (m, 1H), 1.02 (d, J = 6.7 Hz, 6H); 13C NMR (100 MHz, CDCl3): δ 152.1, 150.7, 145.3, 138.0, 130.1, 123.7, 117.0, 41.4, 36.4, 26.9, 22.6; MS (ESI) [M+H]+: m/z 267.1127. Decanal (3m).30 Using Procedure A afforded 0.14 g (91% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 9.76 (t, J = 1.9 Hz, 1H), 2.41 (td, J = 7.4, 1.9 Hz, 2H), 1.82−1.56 (m, 2H), 1.45−1.19 (m, 12H), 0.86 (t, J = 8 Hz, 3H); 13C NMR (100 MHz, CDCl3): δ 203.1, 44.1, 32.0, 29.53, 29.50, 29.4, 29.3, 22.8, 22.4, 14.2; GCMS (EI): m/z 156. Palmitaldehyde (3n).31 Using Procedure A afforded 0.22 g (93% yield) of the desired product as an off-white solid. 1H NMR (400 MHz, CDCl3): δ 9.76 (t, J = 1.9 Hz, 1H), 2.41 (td, J = 7.4, 1.9 Hz, 2H), 1.80−1.52 (m, 2H), 1.47−1.13 (m, 24H), 0.87 (t, 3H); 13C NMR (100 MHz, CDCl3): δ 203.1, 44.1, 32.1, 29.8, 29.7, 29.6, 29.5, 29.3, 22.9, 22.3, 14.3; GCMS (EI): m/z 240. Benzyl (S)-(1-oxo-3-Phenylpropan-2-yl)carbamate (3o).32 Using Procedure A afforded 0.25 g (89% yield) of the desired product as an off-white solid. [α]23D = −52 (c 1, MeOH) (Lit.:15 [α]20D = −51.3 (c 1, MeOH)); 1H NMR (400 MHz, CDCl3): δ 9.67 (s, 1H), 7.81−7.25 (m, 9H), 7.17 (d, J = 8 Hz, 2H), 5.33 (s, 1H), 5.14 (s, 2H), 4.55 (q, J = 6.7 Hz, 1H), 3.17 (d, J = 6.6 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 199, 156.0, 136.2, 135.5, 129.4, 129, 128.7, 128.4, 128.3, 127.3, 67.3, 61.2, 35.5; MS (APCI) [M−H]+: m/z 282.2832. Acetophenone (5a).33 Using Procedure A afforded 0.11 g (94% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 7.97−7.95 (m, 2H), 7.59−7.54 (m, 1H), 7.48−7.44 (m, 2H), 2.61 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 198.3, 137.2, 133.2, 128.7, 128.4, 26.8; GCMS (EI): m/z 120. 1-(4-Methoxyphenyl)ethan-1-one (5b).34 Using Procedure A afforded 0.14 g (92% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 7.93 (d, J = 8.9 Hz, 2H), 6.92 (d, J = 8.8 Hz, 2H), 3.86 (s, 3H), 2.55 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 196.9, 163.6, 130.7, 130.5, 113.8, 55.6, 26.5; GCMS (EI): m/z 150. 1-(4-Bromophenyl)ethan-1-one (5c).33 Using Procedure A afforded 0.18 g (93% yield) of the desired product as an off-white solid. 1 H NMR (400 MHz, CDCl3): δ 7.82 (d, J = 8.5 Hz, 2H), 7.61 (d, J = 8.6 Hz, 2H), 2.58 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 197.1, 136.0, 132.0, 130.0, 128.4, 26.7; GCMS (EI): m/z 198. Benzophenone (5d).27 Using Procedure A afforded 0.17 g (93% yield) of the desired product as a colorless solid. 1H NMR (400 MHz, CDCl3): δ 7.83−7.80 (m, 4H), 7.61−7.57 (m, 2H), 7.51−7.46 (m, 4H); 13C NMR (100 MHz, CDCl3): δ 196.8, 137.7, 132.5, 130.2, 128.4; MS (ESI) [M+H]+: m/z 183. 2,2-Dimethyl-1-phenylpropan-1-one (5e).21 Using Procedure A afforded 0.15 g (93% yield) of the desired product as a colorless oil. 1H NMR (400 MHz, CDCl3): δ 7.69 (d, J = 6.9 Hz, 2H), 7.56−7.35 (m, 3H), 1.35 (s, 9H); 13C NMR (100 MHz, CDCl3): δ 209.4, 138.8, 130.9, 128.2, 128, 44.4, 28.2. GCMS (EI): m/z 162. Adamantan-2-one (5f).21 Using Procedure A afforded 0.13 g (89% yield) of the desired product as a colorless solid. 1H NMR (400 MHz, CDCl3): δ 2.53 (s, 2H), 2.09−1.92 (m, 12H); 13C NMR (100 MHz, CDCl3): δ 218.6, 47.1, 39.4, 36.4, 27.6; GCMS (EI): m/z 150. (S)-2-Phenylcyclohexan-1-one (5g).31 Using Procedure A afforded 0.16 g (82% yield) of the desired product as an off-white solid. [α]24D = −106 (c 0.34, CHCl3) (Lit.:31 [α]25D = −103.4 (c 0.32, CHCl3); 1H NMR (400 MHz, CDCl3): δ 7.39−7.30 (m, 2H), 7.30−7.22 (m, 1H),

7.20−7.07 (m, 2H), 3.62 (dd, J = 12.1, 5.4 Hz, 1H), 2.92−2.39 (m, 2H), 2.28 (m, 1H), 2.23−1.94 (m, 3H), 1.93−1.73 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 210.4, 138.9, 128.7, 128.5, 127.0, 57.5, 42.4, 35.2, 28, 25.5; GCMS (EI): m/z 174. 1-Phenylpropan-2-one (5h).35 Using Procedure A afforded 0.12 g (87% yield) of the desired product as a colorless liquid. 1H NMR (400 MHz, CDCl3): δ 7.37−7.32 (m, 2H), 7.31−7.25 (m, 1H), 7.24−7.19 (m, 2H), 3.70 (s, 2H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 206.6, 134.4, 129.5, 128.9, 127.2, 51.2, 29.4; GCMS (EI): m/z 134. 1-(2,4-Dinitrophenyl)-2-(propan-2-ylidene)hydrazine (5i).36 Using Procedure C afforded 0.2 g (85% yield) of the desired product as an orange solid. 1H NMR (400 MHz, CDCl3): δ 11.05 (s, 1H), 9.15 (d, J = 2.6 Hz, 1H), 8.32 (ddd, J = 9.6, 2.6, 0.8 Hz, 1H), 7.98 (d, J = 9.6 Hz, 3H), 2.20 (s, 3H), 2.11 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 155.3, 145.3, 137.8, 130.2, 123.7, 116.5, 25.7, 17.2; HRMS (ESI): m/z calcd for C9H11N4O4 [M+H]+: 239.0775; found, 239.0776. ((4-(Dimethyliminio)pyridin-1(4H)-yl)sulfonyl)(methoxycarbonyl)amide (6a). This compound was prepared according to a modified literature procedure.37 To a solution of methanol (0.28 mL, 7.06 mmol) in CH2Cl2 (10 mL) at 0 °C was added chlorosulfonylisocyanate (1 g, 7.06 mmol) dropwise (∼10 min). Once the addition was complete, 4-dimethylaminopyridine (1.72 g, 14.12 mmol) was added. After stirring the resulting mixture at ambient temperature for 2 h, it was diluted with H2O. The organic layer was isolated and the aqueous layer was washed twice with CH2Cl2 (30 mL). The combined organic layers were washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure to afford 1.42 g (78%) of 6a as off-white solid. m.p.: 161−163 °C; IR (ATR): νco 1662, 1627, 1560, 1437, 1325, 1270, 1107, 1048; 1H NMR (400 MHz, DMSO-d6): δ 8.47 (d, J = 8.0 Hz, 2H), 6.97 (d, J = 8.0 Hz, 2H), 3.39 (s, 3H), 3.23 (s, 6H); 13C NMR (100 MHz, DMSO-d6): δ 158.4, 156.6, 139.0, 138.4, 107, 106.3, 51.9, 40.2, 40.1, 39.9, 39.7, 39.5, 39.3, 39.1, 38.9; HRMS (ESI): m/z calcd for C9H14N3O4S [M+H]+, 260.0700; found, 260.0704. (Methoxycarbonyl)(pyridin-1-ium-1-ylsulfonyl)amide (6b). To a solution of chlorosulfonylisocyanate (1 g, 7.06 mmol) in benzene (6 mL) at 0 °C was added a solution of methanol (0.28 mL, 7.06 mmol) in benzene (4 mL) over the course of 30 min. Once the addition was complete, residual solvent was removed under reduced pressure to give the desired sulfamoyl chloride intermediate as a white solid (1.15 g). A solution of the newly formed sulfamoyl chloride (1.15 g, 6.64 mmol) in benzene (8 mL) was added dropwise to a solution of pyridine (1 mL, 13.2 mmol) in benzene (10 mL) at 25 °C. After the addition was complete (∼1 h), 20 mL of H2O was added and the resulting mixture was extracted twice with EtOAc (30 mL). The organic layer was separated, washed with brine and the solvent was removed under reduced pressure to afford 0.93 g (65%) of 6b as a white solid. m.p.: 109−111 °C; IR (ATR): νco 3077, 1729, 1607, 1532, 1211, 1043; 1H NMR (400 MHz, CDCl3): δ 9.33 (d, J = 5.5 Hz, 2H), 8.41 (t, J = 7.7 Hz, 1H), 7.95 (t, J = 6.9 Hz, 2H), 3.59 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 159.1, 145.5, 141.5, 126.7, 53.2; HRMS (ESI): m/z calcd for C7H9N2O4S [M+H]+, 217.0278; found, 217.0278. (Methoxycarbonyl)((1-methyl-1H-imidazol-3-ium-3-yl)sulfonyl)amide (6c). To a solution of methanol (0.28 mL, 7.06 mmol) in CH2Cl2 (10 mL) at 0 °C was added chlorosulfonylisocyanate (1 g, 7.06 mmol) dropwise (∼10 min). Once the addition was complete, 1methylimidazole (1.6 g, 14.12 mmol) was added. After stirring the resulting mixture at ambient temperature for 2 h, it was diluted with H2O. The organic layer was isolated and the aqueous layer was washed twice with CH2Cl2 (30 mL). The combined organic layers were washed with brine, dried over anhydrous Na2SO4, and concentrated under reduced pressure to afford 1.44 g (93%) of 6a as an off-white solid. m.p = 142−144 °C; IR (ATR): νco 3133, 1651, 1439, 1314, 1297, 1105, 1086; 1H NMR (400 MHz, acetone-d6): δ 9.05 (s, 1H), 7.72 (t, J = 1.8 Hz, 1H), 7.59 (t, J = 1.8 Hz, 1H), 4.12 (s, 3H), 3.46 (s, 3H); 13C NMR (100 MHz, acetone): δ 206.1, 159.9, 137.6, 123.6, 121.7, 52.3, 36.6; HRMS (ESI): m/z calcd for C6H10N3O4S [M+H]+, 220.0387; found, 220.0396. E

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry Methyl (E,4S)-4-((tert-Butoxycarbonyl)amino)-6-methylhept-2enoate (7a).17 Using Procedure D afforded 0.2 g (78% yield) of the desired product as a colorless oil. [α]23D = −18 (c 1, CHCl3) (Lit.:17 [α]25D = −17 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3): δ 6.86 (dd, J = 15.6, 5.5 Hz, 1H), 5.94 (dd, J = 15.7, 1.5 Hz, 1H), 4.68−4.23 (m, 2H), 3.75 (s, 3H), 1.71 (dt, J = 13.4, 6.7 Hz, 1H), 1.46 (s, 9H), 1.40 (t, J = 7.3 Hz, 2H), 0.95 (d, J = 6.6 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 167, 155.2, 149.4, 120.1, 79.9, 51.8, 48, 43.9, 28.5, 24.9, 22.8, 22.3; HRMS (ESI): m/z calcd for C14H25NO4Na [M+Na]+, 294.1676; found, 294.1711. Methyl (E,4S)-4-(((Benzyloxy)carbonyl)amino)pent-2-enoate (7b). Using Procedure D afforded 0.22 g (83% yield) of the desired product as an off-white solid. m.p.: 45−47 °C; [α]23D = −18 (c 1, CHCl3); IR (ATR): νco 3277, 2952, 1709, 1690, 1540; 1H NMR (400 MHz, CDCl3): δ 7.60−7.29 (m, 5H), 6.88 (dd, J = 15.7, 5.1 Hz, 1H), 6.08−5.79 (m, 1H), 5.35−4.99 (m, 2H), 4.77 (d, J = 8.2 Hz, 1H), 4.65−4.40 (m, 1H), 3.73 (s, 3H), 1.29 (d, J = 7.0 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 166.8, 155.5, 149.1, 136.3, 128.7, 128.4, 128.3, 120.2, 67.1, 51.8, 47.7, 20.4; HRMS (ESI): m/z calcd for C14H17NO4Na [M+Na]+, 286.1050; found, 286.1079. Methyl (E,4S)-4-(((Benzyloxy)carbonyl)amino)-5-phenylpent-2enoate (7c). Using the Procedure D afforded 0.28 g (82% yield) of the desired product as an off-white solid. m.p.: 75−77 °C; [α]23D = −4 (c 1, CHCl3); IR (ATR): νco 3320, 2923, 1715, 1690, 1532; 1H NMR (400 MHz, CDCl3): δ 7.47−7.23 (m, 8H), 7.22−7.14 (m, 2H), 6.95 (dd, J = 15.7, 5.1 Hz, 1H), 5.89 (dd, J = 15.7, 1.6 Hz, 1H), 5.09 (d, J = 2.1 Hz, 2H), 4.88−4.57 (m, 2H), 3.75 (s, 3H), 2.95 (d, J = 6.1 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 166.6, 155.6, 147.4, 136.3, 136.1, 129.5, 128.8, 128.7, 128.4, 128.3, 127.2, 121.1, 77.5, 77.2, 76.8, 67.1, 52.9, 51.8, 40.7; HRMS (ESI): m/z calcd for C20H21NO4Na [M +Na]+, 362.1363; found, 362.1374. Kinetics Data. An oven-dried NMR tube was charged with the Burgess reagent (0.028 mmol) followed by a solution of an alcohol (0.0212 mmol) and 1,3,5-trimethoxybenzene (0.0212 mmol) (as an internal standard) in DMSO-d6 (0.6 mL). Conversions of the alcohols to their respective oxidized products were independently monitored over time using 1H NMR spectroscopy. Competition Experiments. An oven-dried NMR tube was charged with various alcohols (0.1 mmol each) and DMSO-d6 (0.6 mL). The Burgess reagent (0.13 mmol) was added to the NMR tube and the conversions of the alcohols to their respective oxidized products were independently monitored using 1H NMR spectroscopy.

■

Chem. Soc. 1972, 94, 6135. (d) Burgess, E. M.; Penton, H. R.; Taylor, E. A. J. Org. Chem. 1973, 38, 26. (e) Burgess, E. M.; Penton, H. R., Jr.; Taylor, E. A.; Williams, W. M. Org. Synth. 1977, 56, 40. (f) Duncan, J. A.; Hendricks, R. T.; Kwong, K. S. J. Am. Chem. Soc. 1990, 112, 8433. (g) Franck-Neumann, M.; Miesch, M.; Kempf, H. Tetrahedron 1987, 43, 853. (2) (a) Claremon, D. A.; Phillips, B. T. Tetrahedron Lett. 1988, 29, 2155. (b) Jose, B.; Sulatha, M. S.; Madhavan Pillai, P.; Prathapan, S. Synth. Commun. 2000, 30, 1509. (c) Nemoto, H.; Kubota, Y.; Yamamoto, Y. J. Org. Chem. 1990, 55, 4515. (d) Miller, C. P.; Kaufman, D. H. Synlett 2000, 2000, 1169. (3) Creedon, S. M.; Crowley, H. K.; McCarthy, D. G. J. Chem. Soc., Perkin Trans. 1 1998, 1015. (4) (a) Maugein, N.; Wagner, A.; Mioskowski, C. Tetrahedron Lett. 1997, 38, 1547. (b) Sajitha, T. S.; Prathapan, S.; Unnikrishnan, P. A. RSC Adv. 2014, 4, 44689. (5) (a) Wipf, P.; Miller, C. P. Tetrahedron Lett. 1992, 33, 907. (b) Tavares, F.; Lawson, J. P.; Meyers, A. I. J. Am. Chem. Soc. 1996, 118, 3303. (c) Wipf, P.; Fritch, P. J. Am. Chem. Soc. 1996, 118, 12358. (d) Wipf, P.; Venkatraman, S. Tetrahedron Lett. 1996, 37, 4659. (e) Wipf, P.; Hayes, G. B. Tetrahedron 1998, 54, 6987. (f) Brain, T. C.; Paul, J. M.; Loong, Y.; Oakley, P. J. Tetrahedron Lett. 1999, 40, 3275. (g) Wipf, P.; Miller, C. P.; Venkatraman, S.; Fritch, P. C. Tetrahedron Lett. 1995, 36, 6395. (h) Brain, C. T.; Paul, J. M. Synlett 1999, 1999, 1642. (6) (a) Toupet, L.; Barragan, V.; Dewynter, G.; Montero, J.-L. Org. Lett. 2001, 3, 2241. (b) Armitage, I.; Berne, A. M.; Elliott, E. L.; Fu, M.; Hicks, F.; McCubbin, Q.; Zhu, L. Org. Lett. 2012, 14, 2626. (7) (a) Rinner, U.; Adams, D. R.; dos Santos, M. L.; Hudlicky, T.; Abboud, K. A. Synlett 2003, 1247. (b) Metcalf, T. A.; Simionescu, R.; Hudlicky, T. J. Org. Chem. 2010, 75, 3447. (c) Sullivan, B.; Gilmet, J.; Leisch, H.; Hudlicky, T. J. Nat. Prod. 2008, 71, 346. (8) (a) Rigby, J. H.; Mateo, M. E. J. Am. Chem. Soc. 1997, 119, 12655. (b) Dolle, R. E.; Nicolaou, K. C. J. Am. Chem. Soc. 1985, 107, 1691. (c) Daniewski, A. R.; Wovkulich, P. M.; Uskokovic, M. R. J. Org. Chem. 1992, 57, 7133. (d) Holton, R. A.; Kim, H. B.; Somoza, C.; Liang, F.; Biediger, R. J.; Boatman, P. D.; Shindo, M.; Smith, C. C.; Kim, S. J. Am. Chem. Soc. 1994, 116, 1599. (9) (a) Nicolaou, K. C.; Snyder, S. A.; Nalbandian, A. Z.; Longbottom, D. A. J. Am. Chem. Soc. 2004, 126, 6234. (b) Nicolaou, K. C.; Huang, X.; Snyder, S. A.; Rao, P. B.; Bella, M.; Reddy, M. V. Angew. Chem., Int. Ed. 2002, 41, 834. (c) Nicolaou, K. C.; Longbottom, D. A.; Snyder, S. A.; Nalbanadian, A. Z.; Huang, X. Angew. Chem., Int. Ed. 2002, 41, 3866. (10) (a) Burckhardt, S. Synlett 2000, 2000, 559. (b) Lamberth, C. J. J. Prakt. Chem. 2000, 342, 518. (11) Parikh, J. R.; Doering, W. v. E. J. Am. Chem. Soc. 1967, 89, 5505. (12) (a) Mancuso, A. J.; Huang, S.-L.; Swern, D. J. Org. Chem. 1978, 43, 2480. (b) Omura, K.; Swern, D. Tetrahedron 1978, 34, 1651. (13) The Burgess reagent has been reported to oxidize benzoin derivatives in yields of up to 67% in dry CH2Cl2; see: Jose, B.; Unni, M. V. V.; Prathapan, S.; Vadakkan, J. J. Synth. Commun. 2002, 32, 2495. Rappai, J. P.; Karthikeyan, J.; Prathapan, S.; Unnikrishnan, P. A. Synth. Commun. 2011, 41, 2601. In our hands, the oxidation of benzyl alcohol to benzaldehyde was not observed when subjected to similar conditions. (14) The Burgess reagent is commercially available but can be conveniently prepared on the multigram scale from chlorosulfonyl chloride, CH3OH and Et3N; see ref 1d. (15) The [α]23D of 3o was measured to be −52 (c 1, MeOH) and was in agreement with the literature value ([α]20D = −51.3, c 1, MeOH); see: De Luca, L.; Giacomelli, G.; Porcheddu, A. Org. Lett. 2001, 3, 3041. (16) Subjecting tert-butanol to the reaction conditions resulted in the formation of an unidentified product; the formation of olefins or thioacetals were not observed by NMR spectroscopy. (17) The [α]23D of 7a was measured to be −18 (c 1, CHCl3) and was in agreement with the literature value ([α]25D = −17, c 1, CHCl3); see: Kokotos, G.; Six, D. A.; Loukas, V.; Smith, T.; ConstantinouKokotou,

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.6b02629. Kinetics data and NMR spectra (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Christopher W. Bielawski: 0000-0002-0520-1982 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We are grateful to the IBS (IBS-R019-D1) and the BK21 Plus Program as funded by the Ministry of education and the National Research Foundation of Korea for financial support

■

REFERENCES

(1) (a) Atkins, G. M.; Burgess, E. M. J. Am. Chem. Soc. 1968, 90, 4744−4745. (b) Burgess, E. M.; Penton, H. R.; Taylor, E. A. J. Am. Chem. Soc. 1970, 92, 5224. (c) Atkins, G. M.; Burgess, E. M. J. Am. F

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX

Article

The Journal of Organic Chemistry V.; Hadjipavlou-Litina, D.; Kotsovolou, S.; Chiou, A.; Beltzner, C. C.; Dennis, E. A. J. Med. Chem. 2004, 47, 3615. (18) The Burgess reagent was found to decompose in DMSO over time. Moreover, the product yield appeared to be dependent on the quantity of undecomposed Burgess reagent present. For example, exposure of BnOH to a DMSO solution of 1 that was ca. 50% decomposed afforded ca. 50% yield of benzaldehyde. The formation of benzaldehyde was not observed when BnOH was exposed to a solution of 1 that was fully decomposed. (19) Pfitzner, K. E.; Moffatt, J. G. J. Am. Chem. Soc. 1963, 85, 3027. (20) Wang, A.; Jiang, H. J. Org. Chem. 2010, 75, 2321. (21) Steves, J. E.; Stahl, S. S. J. Am. Chem. Soc. 2013, 135, 15742. (22) Jiang, X.; Wang, J. M.; Zhang, Y.; Chen, Z.; Zhu, Y. M.; Ji, S. J. Org. Lett. 2014, 16, 3492. (23) Correa, A.; Martin, R. J. J. Am. Chem. Soc. 2009, 131, 15974. (24) Xu, B.; Lumb, J.-P.; Arndtsen, B. A. Angew. Chem., Int. Ed. 2015, 54, 4208. (25) Mangawa, S. K.; Bagh, S. K.; Sharma, K.; Awasthi, S. K. Tetrahedron Lett. 2015, 56, 1960. (26) Feng, Q.; Song, Q. J. Org. Chem. 2014, 79, 1867. (27) Dai, W.; Lv, Y.; Wang, L.; Shang, S.; Chen, B.; Li, G.; Gao, S. Chem. Commun. 2015, 51, 11268. (28) Hon, Y.-S.; Chang, F.-J.; Lu, L.; Lin, W.-C. Tetrahedron 1998, 54, 5233. (29) Lue, P.; Fan, W.-Q.; Zhou, X.-J. Synthesis 1989, 1989, 692. (30) Zhao, Y.-G.; Snieckus, V. Org. Lett. 2014, 16, 390. (31) Zhu, Y.; Zhao, B.; Shi, Y. Org. Lett. 2013, 15, 992. (32) Doherty, W.; Evans, P. J. Org. Chem. 2016, 81, 1416. (33) Zhang, G.; Hanson, S. K. Org. Lett. 2013, 15, 650. (34) Maji, T.; Karmakar, A.; Reiser, O. J. Org. Chem. 2011, 76, 736. (35) Yoshimura, A.; Nguyen, K. C.; Klasen, S. C.; Saito, A.; Nemykin, V. N.; Zhdankin, V. V. Chem. Commun. 2015, 51, 7835. (36) Chen, J.; Wu, W.; McNeil, A. J. Chem. Commun. 2012, 48, 7310. (37) Toupet, L.; Barragan, V.; Dewynter, G.; Montero, J.-L. Org. Lett. 2001, 3, 2241.

G

DOI: 10.1021/acs.joc.6b02629 J. Org. Chem. XXXX, XXX, XXX−XXX