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Note Cite This: J. Org. Chem. 2017, 82, 11218-11224

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Iron-Catalyzed Asymmetric Nitro-Mannich Reaction Agata Dudek and Jacek Mlynarski*,†,‡ †

Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

‡

S Supporting Information *

ABSTRACT: The first enantioselective addition of nitroalkanes to imines (nitro-Mannich reaction), mediated by an iron(II) catalyst assembled by a hindered hydroxyethyl-pybox ligand, is described. This valuable carbon−carbon bond-forming reaction proceeds smoothly at room temperature to afford enantioenriched β-nitro amines in good yields and high enantioselectivity, up to 98% with unprecedentedly low iron catalyst loading (5 mol %).

C

Scheme 1. Examples of Nitro-Mannich Reaction Promoted by Zn- and Cu-Based Catalysts

atalytic asymmetric nitro-Mannich (or aza-Henry) reaction involving nucleophilic addition of nitroalkanes to imines and related compounds is one of the most fundamental reactions for the synthesis of optically active organic compounds bearing two vicinal nitrogenated functionalities.1 The resulting β-nitro amines are versatile building blocks for transformation into biologically active compounds such as diamines, β-amino alcohols, and α-amino acids. The first example of catalytic enantioselective nitro-Mannich reactions, between N-phosphinoyl imines and nitromethane, was reported by Shibasaki in 1999.2 The use of binaphthoxide(binol)-based heterobimetallic complexes of ytterbium and aluminum designed by Shibasaki opened the way for broad application of hetero- and homobimetallic catalysts3 for the activation of various types of imine substrates. An example of an addition to N-Boc-imines promoted by Trost catalyst (C2)3 is presented in Scheme 1. Alternatively, Jørgensen and co-workers used copper bis(oxazoline) complexes to catalyze the reaction of silyl nitronates with α-imino esters (Scheme 1).4 In 2006, Palomo showed that cooperative activation of nitro compounds and N-Boc aryl imines toward the aza-Henry reaction can be effected by combination of zinc triflate (30 mol %) coordinated by optically pure N-methylephedrine (45 mol %) and a tertiary amine (30 mol %).5 This finding oriented new research toward establishing the validity of this activation model in related reactions but also toward the application of more sustainable reaction conditions and catalysts for this reaction. However, all of the above-mentioned examples require a high catalyst (20 or even 30 mol %) and chiral ligand (20−45%) loading, while the substrate scope was limited with regards to one or both of the reaction partners. The alternative organocatalytic asymmetric nitro-Mannich reactions have been also reported by Johnston,6 Takemoto,7 Zhou,8 and Jacobsen9 featuring, however, some important restrictions regarding the substrate scope. While previous works of Trost3 and Palomo5 addressed the application of environmentally benign zinc-based catalysts, nothing is known about more demanding but also more desirable ironbased catalytic enantioselective aza-Henry reaction. In spite of © 2017 American Chemical Society

the recent statement that “iron catalysis is potentially capable of covering almost the entire range of organic synthesis”,10a to the best of our knowledge this fundamental asymmetric transformation has never been reported by using chiral iron catalysts. In this paper, we present the first example of asymmetric nitroMannich reaction driven by chiral Fe(II) complex thus Received: July 18, 2017 Published: October 2, 2017 11218

DOI: 10.1021/acs.joc.7b01786 J. Org. Chem. 2017, 82, 11218−11224

Note

The Journal of Organic Chemistry providing new application of this metal in asymmetric synthesis. Presented concept of substrate activation requires small catalytic amount of metal salt and chiral ligand and is superior to previously published protocols in terms of reaction efficiency. Previously, we showed that iron(II) chloride in a combination with chiral pybox ligand can control enantioselective carbon− carbon bond formation in the asymmetric Mukaiyama reaction.11 Assuming that iron complexes can also control the addition to the imine group, we started an extensive investigation for a practical and efficient catalyst capable of activating reagents in the nitro-Mannich reaction. Our new finding is that only 5 mol % of Fe(OTf)2 coordinated by hindered pybox ligand (L7) can effect highly enantioselective aza-Henry reactions (Scheme 1) of nitromethane and imines, thus providing a new and extremely practical entry to enantioenriched diamines. Moreover, while a wide range of transition-metal complexes with pybox-type ligands12 have been incorporated for the series of catalytic stereoselective transformations,13−16 this commonly used ligand has not been investigated in the nitro-Mannich reaction. Our initial aim was to identify the best-suited iron complex in terms of both reaction conversion and enantioselection. For this purpose, we initiated work by evaluating reaction of N-Boc-imine (1a) with nitromethane under the conditions reported previously by Palomo5 by replacing zinc in the iron salt. Unfortunately, the application of iron(II) salts with various bidentate ligands, including (−)-N-methylephedrine for the reaction of N-Boc-protected aldimine, was entirely unsuccessful. More promising results were gained after exchanging amine ligand for commercial (S,S)-iPr-pybox (L1) in an in situ combination with iron triflate (Table 1). However, the observed reaction yield and enantioselectivity highly depend on the imine substrate (Table 1, entries 1−3). During the study, we found that the most important objective was to identify the bestsuited N-protecting group in the imine component. Thus, a series of N-protected aldimines (1a−c) were reacted with nitromethane in the presence of 10 mol % of Fe(OTf)2, ligand L1, and triethylamine in THF. Encouraging outcomes were observed when N-Boc-imine (1a) or N-phosphinoylimine (1c) were applied in the reaction, whereas the N-benzhydryl group (1b) turned out to be unreactive under reaction conditions. Interestingly, while the reaction of N-Boc-imine (1a) led to racemic product 2a, addition of nitromethane to 1c resulted in synthesis of the desired amine with a high level of enantioselectivity (Table 1, entry 3). These observations verified that the presence of the phosphinoyl moiety is a key for success, but there was still much room for the improvement in terms of reaction enantioselectivity. Having the best type of imine in hand, we began to investigate the reaction enantioselectivity under control of structurally modified pybox ligands collected in Figure 1. As the results in Table 1 show, the Ph-pybox (L2) and Inda-pybox (L3) in a combination with Fe(OTf)2 were superior to commercially available ligands. The highest enantioselectivity (92%) was obtained in the reaction with L3, which furnishes the corresponding product in 77% yield (Table 1, entry 5). To our delight, catalyst loading could also be reduced from 10 to 5 mol %. Thus, application of the same iron catalyst with ligand L3 in 10 and 5 mol % gave selectivities of 92% and 90%, while the reaction yield was even better when a lower amount of catalyst was used (Table 1, entry 5 vs 6). It is important to mention that all the reactions proceeded at room temperature without any detrimental effect on the reaction outcome.

Table 1. Initial Screening of Iron Salt and Ligands in Asymmetric Nitro-Mannich Reactions of Series of N-Protected Iminesa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

imine

Lewis acid

cat. (mol %)

ligand

yieldb (%)

eec (%)

1a 1b 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c 1c

Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 Fe(OTf)2 FeCl2 Zn(OTf)2 Zn(OTf)2 Cu(OTf)2

10 10 10 10 10 5 10 10 10 10 5 1 10 10 10 10 10 5 10

L1 L1 L1 L2 L3 L3 L4 L5 L6 L7 L7 L7 L8 L9 L10 L7 L7 L7 L7

74 0 55 71 77 87 67 84 76 80 83 trace 87 31 82 0 81 90 21

rac 65 87 92 90 83 82 70 93 96 79 58 75 84 65 47

a

Reaction conditions: imine (0.4 mmol), Lewis acid (5−10 mol %), pybox-type ligand (5−10 mol %), NO2Me (10 equiv), TEA (0.5 equiv), 0.5 mL of THF, 2 h, rt. bIsolated yields after column chromatography. c Determined by HPLC.

Figure 1. Series of pybox ligands tested in nitro-Mannich reactions.

Considering further improvement of the reaction enantioselectivity, a series of modified pybox ligands (L4−10) was evaluated in association with Fe(OTf)2 to identify the most enantioselective and reliable system. Ligands prepared from serine (L4−6) and more hindered ones incorporating threonine moieties (L7−10) were tested in the nitro-Mannich reaction (Table 1, entries 7−15). Although in all cases the reaction proceeded smoothly to give β-nitro amine product 2c in good yields, observed enantioselectivities varied with the ligand structure. The best results in terms of ee (93%) and high yield were reported in the presence of tert-butyldiphenylsilyl-protected hydroxyethyl-pybox (TPShe-pybox) L7 (Table 1, entry 10). 11219

DOI: 10.1021/acs.joc.7b01786 J. Org. Chem. 2017, 82, 11218−11224

Note

The Journal of Organic Chemistry Conspicuously, bulky groups attached to the oxygen atom play a crucial role in asymmetric induction and reaction efficiency. In this case, decreasing of the catalyst loading to 5 mol % has a progressive effect on the reactivity and enantioselectivity of the reaction at hand (Table 1, entry 11). Further decreasing the catalyst loadings to 1 or 2 mol % was not promising (Table 1, entry 12). Accordingly, the best reaction conditions (5 mol % of Fe(OTf)2 and TPS-he-pybox ligand (L7)) furnished the β-nitro amine 2c in 83% yield and with 96% ee in 2 h at room temperature (Table 1, entry 11). Application of iron(II) chloride (Table 1, entry 16) as well as iron(III) salts was not promising. It is also noteworthy that zinc triflate with the same L7 ligand in combination with trimethylamine was also found to be reactive, yet the reaction outcome was less promising in comparison to iron-based catalyst (Table 1, entry 17). To test the reaction scope, a representative selection of N-phosphinoyl-protected aryl imines was subjected to the optimized reaction conditions (5 mol % of Fe(OTf)2-TPS-hepybox catalyst, at room temperature). As presented in Figure 2, the proposed system allowed the formation of β-nitro amines with very good yields and excellent enantioselectivities in all tested cases. Imines, which bear electron-withdrawing substituents (4c−g), were more reactive than those with electron-donating groups (4a,b); however, the products were formed with the same control of enantioselectivity. What is more, the obtained results for aromatic imine substrates possessing groups placed in the ortho, meta, and para position (4e−g) suggest that electronic perturbations are not significant for yields and ee values. Moreover, the proposed catalytic system suitable for asymmetric nitro-Mannich reaction of heteroaromatic, bicyclic, and α,β-unsaturated substrates (4h−j) afforded the desired product with good yields and ee, up to 98%. Finally, the proposed ironbased catalytic system was applied for higher order nitroalkanes. All of the tested substrates except nitroethanol (4m) gave products with acceptable yield and a high level of enantioselectivity in the range of 90% (4k,l,n). In summary, we have demonstrated a new strategy for asymmetric nitro-Mannich (aza-Henry) reaction of aldimines using an iron(II)-TPS-he-pybox complex. The application of only 5 mol % of this in situ formed chiral catalyst for a broad scope of substrates resulted in formation of corresponding β-nitro amines with high yields and excellent enantioselectivities, surpassing results obtained for commercially available ligands. It is noteworthy that the reaction proceeded at room temperature without any detrimental effect in the reaction outcome while high catalyst activity and enantioselectivity remains at high level. Elaborated methodology requires small catalytic amount of metal salt and chiral ligand surpassing previously published protocols in terms of reaction efficiency and sustainability.

■

Figure 2. Asymmetric nitro-Mannich reaction catalyzed by iron(II)TPS-he-pybox complex. (a) 10 mol % of catalyst. 13

C NMR spectra were recorded with 600 MHz (1H) and referenced relative to tetramethylsilane (δ = 0 ppm) for 1H NMR and CDCl3 (δ = 77.16 ppm) for 13C NMR. Data are reported as follows: chemical shift, multiplicity (br s = broad singlet, s = singlet, d = doublet, t = triplet, q = quartet, qui = quintet, m = multiplet), and integration. High-resolution mass spectra (HRMS) were recorded with an electrospray ionization time-of-flight (ESI-TOF) mass spectrometer. Infrared (IR) spectra were recorded with a Fourier transform infrared (FT-IR) spectrometer and are reported in wave numbers (cm−1).Optical rotations were measured at room temperature with a digital polarimeter. HPLC analysis were performed using OD-H and OZ-H columns with UV detection at 220 nm. L-Serine-based ligands L4−L6 were synthesized by according to the literature procedure:11,17 Preparation of Silylated Bis(hydroxymethyl)pyridine (L4−L6). To a to suspension of bis(hydroxymethyl)pyridine (0.5 mmol, 1 equiv) in methylene chloride was added 2 mL of imidazole (22.9 mmol, 4.6 equiv) at rt followed by addition of silyl chloride (1,5 mmol, 3 equiv) in one portion. The resulting mixture was stirred for 15 h at rt. The white suspension was purified by column chromatography on silica gel (EA/Hx, 1:1) to give the desired silylated ligands L4−L6.

EXPERIMENTAL SECTION

General Information. All starting materials and reagents were purchased from commercial sources and used without purification. Dry THF was distilled from potassium to prior to use. All catalytic reactions were performed under inert atmosphere. Reactions were controlled by analytical thin-layer chromatography (TLC) using Merck silica gel 60 F254 precoated plates. All reagents and solvents were purified and dried according to common methods. All organic solutions were dried over anhydrous magnesium sulfate (MgSO4). Reaction products were purified by normal-phase flash chromatography in air using silica gel 60 (230−400 mesh) with n-Hx (Hx) and ethyl acetate (EA) as eluents, unless otherwise stated. 1H and 11220

DOI: 10.1021/acs.joc.7b01786 J. Org. Chem. 2017, 82, 11218−11224

Note

The Journal of Organic Chemistry TPS-me-pybox (L4).18 Compound L4 was obtained as a white solid 240 mg, yield 88%; purified by column chromatography with EA/Hx, 1:1; [α]D25 = +122.8 (c = 1.0, CHCl3) [lit.18 [α]D25 = +117.0 (c = 1.0, CH2Cl2)]; 1H NMR (600 MHz, CDCl3) δ 8.12 (d, J = 7.8 Hz, 2H), 7.82 (t, J = 7.6 Hz, 1H), 7.67−7.65 (m, 8H), 7.42−7.34 (m, 12H), 4.62−4.56 (m, 4H), 4.52−4.47 (m, 2H), 3.95 (dd, J = 9.8, 3.4 Hz, 2H), 3.76 (dd, J = 10.2, 3.6 Hz, 2H), 1.02 (s, 18H); 13C NMR (151 MHz, CDCl3) δ 163.8, 147.0, 137.3, 135.8, 135.7, 133.6, 133.4, 129.9, 127.9, 127.8, 125.9, 71.3, 68.6, 65.8, 26.9, 19.4. TBS-me-pybox (L5): 17 Compound L5 was obtained as a white solid, 197 mg, yield 78%; purified by column chromatography with EA/Hx, 1:1; [α]D25 = +76.2 (c = 1.0, CHCl3) [lit.17 [α]D18.5 = +105.9 (c = 1.0, CH2Cl2)]; 1H NMR (600 MHz, CDCl3) δ 8.16 (d, J = 7.8 Hz, 2H), 7.86 (t, J = 7.6 Hz, 1H), 4.56 (dt, J = 9.2, 7.9 Hz, 2H), 4.49−4.43 (m, 4H), 3.93 (dd, J = 10.2, 3.9 Hz, 2H), 3.65 (dd, J = 5.7, 4.3 Hz, 2H), 0.86 (s, 18H), 0.07 (d, J = 15.8 Hz, 12H); 13C NMR (151 MHz, CDCl3) δ 163.7, 147.0, 137.4, 125.9, 71.4, 68.6, 65.2, 26.0, 18.4. TIPS-me-pybox (L6).18 Compound L6 was obtained as a white solid, 182 mg, yield 62%; purified by column chromatography with EA−Hx, 1:1; [α]D25 = +82.7 (c = 1.0, CHCl3) (lit.18 [α]D23 = +66.8 (c = 1.0, CH2Cl2)]; 1H NMR (600 MHz, CDCl3) δ 8.16 (d, J = 7.3 Hz, 1H), 7.85 (t, J = 7.7, 2H), 4.59−4.54 (m, 4H), 4.50−4.45 (m, 2H), 4.04 (dd, J = 9.8, 4.0 Hz, 2H), 3.72 (dd, J = 9.8, 7.4 Hz, 2H), 1.14−1.04 (m, 42H); 13C NMR (151 MHz, CDCl3) δ 163.8, 147.0, 137.3, 125.9, 71.5, 68.7, 65.6, 18.1, 12.1. L-Threonine-based ligands L7−L10 were obtained according to the literature procedure.11 TPS-he-pybox (L7): 11 white solid, 1006 mg, yield 77%; purified by column chromatography with EA; [α]D25 = −57.0 (c = 1.0, CHCl3) [lit.11 [α]D= −45.1 (c = 1.05, CHCl3)]; 1H NMR (600 MHz, CDCl3) δ 8.10 (d, J = 7.9 Hz, 2H), 7.80 (t, J = 7.80 Hz, 1H), 7.69−7.66 (m, 8H), 7.44−7.40 (m, 4H), 7.37−7.35 (m, 8H), 4.65−4.62 (m, 2H), 4.50−4.42 (m, 4H), 4.28−4.24 (m, 2H), 1.05 (s, 19H), 1.03 (d, J = 6.3 Hz, 6H); 13C NMR (151 MHz, CDCl3) δ 163.4, 147.0, 137.3, 136.0, 135.9, 134.3, 134.0, 129.9, 129.8, 127.8, 127.7, 125.9, 71.6, 70.0, 69.2, 27.1, 19.4, 17.7. TBS-he-pybox (L8): 19 light yellow solid, 166 mg, yield 42%; purified by column chromatography with Hx/EA (2:1); [α]D25 = −57.0 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3) δ 8.18 (d, J = 7.8 Hz, 2H), 7.86 (t, J = 7.6 Hz, 1H), 4.65−4.62 (m, 2H), 4.50−4.54 (m, 2H), 4.48−4.43 (m, 4H), 4.22−4.17 (m, 2H), 1.1 (d, J = 6.1 Hz, 6H), 0.87 (s, 18H), 0.08 (d, J = 4.0 Hz, 12H); 13C NMR (151 MHz, CDCl3) δ 163.4, 147.0, 137.4, 125.9, 72.0, 69.2, 69.0, 25.9, 18.2, 18.02, −4.4, −4.7. MeO-he-pybox (L9): white solid, 210 mg, yield 25%; purified by column chromatography with DCM/EtOH 50:1; [α]D26 = −110.0 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3) δ 8.21 (d, J = 7.9 Hz, 2H), 7.86 (t, J = 7.8 Hz, 1H), 4.59−4.55 (m, 2H), 4.52−4.49 (m, 2H), 4.44,(t, J = 8.3 Hz, 2H) 3.66−3.62 (m, 2H), 3.40 (s, 6H), 1.17 (s, 6H); 13 C NMR (151 MHz, CDCl3) δ 163.5, 146.9, 137.933, 126.1, 77.5, 70.1, 69.4, 57.0, 14.3; FT-IR 3411, 2989, 2935, 2850, 1681, 1573; mp = 105 °C; HRMS (ESI-TOF) calcd for C17H23N3O4Na [M + Na]+ 356.1586, found 356.1568. t BuO-he-pybox (L10): white solid, 320 mg, yield 52%; purified by column chromatography with EA; [α]D24 = −65.5 (c = 1.0, CHCl3); 1 H NMR (600 MHz, CDCl3) δ 8.19 (d, J = 7.8 Hz, 2H), 7.85 (t, J = 7.8 Hz, 1H), 4.61−4.55 (m, 2H), 4.51−4.46 (m, 4H), 4.10−4.03 (m, 2H), 1.21 (s, 18H), 1.05 (d, J = 6.4 Hz, 6H); 13C NMR (151 MHz, CDCl3) δ 163.3, 147.1, 137.3, 125.9, 74.1, 71.5, 69.3, 67.7, 28.5, 17.0; FT-IR 3254, 3067, 2974, 2921, 1633 1380, 1197 1089 cm−1; mp = 161 °C; HRMS (ESI-TOF) calcd for C23H35N3O4Na [M + Na]+ 440.2525, found 440.2538. Preparation of Aldoximes. N-Phosphinylimines were synthesized from the corresponding oximes by the modification of the literature procedure.20 Suspension of hydroxylamine hydrochloride (1.6 equiv), and NaOAc (2.0 equiv) in 80% aqueous EtOH (20.0 mL) was stirred at rt for 30 min. After this time aldehyde (1.0 equiv) was added and the reaction mixture was heated gently to reflux for 30 min. Following cooling to rt, the solvent was evaporated under vacuum and

the residue purified by column chromatography with Hx/EA (9:1) as eluent, to provide crystalline oxime with quantitative yield. Preparation of N-Phosphinylimines.21 In a round bottom flask under inert atmosphere oxime (1.0 equiv) was dissolved in mixture of dry DCM/Hx (1:1) and cooled to −40 °C. To the reaction mixture was added TEA (1.1 equiv) dropwise followed (after 10 min) by addition of Ph2PCl (1.1 equiv). After addition, the reaction mixture was gradually warmed to room temperature and stirred overnight. When the reaction was completed, the contents of the flask were poured over ice and the aqueous phase was extracted with DCM (3 × 15 mL). The combined organic layers were washed with water and brine and dried under anhydrous Na2SO4.The solvents were evaporated under reduced pressure to afford the crude aldimine, which was purified by column chromatography on silica gel with DCM−acetone (9:1) as eluent. The spectral characteristics of N-phosphinylimines 1c,22 3a,22 3b,22 3c,22 3d,22 3e,23 3h,24 3i,23 and 3j25 were consistent with those reported previously in the literature. N-(3-Nitrobenzylidene)-P,P-diphenylphosphine amide (3f): yellow solid, 820 mg, overall yield 35%; 1H NMR (600 MHz, CDCl3) δ 9.41 (d, J = 30.4 Hz, 1H), 8.89 (t, J = 1.7 Hz, 1H), 8.42 (ddd, J = 8.2, 2.3, 1.1 Hz, 1H), 8.26 (dt, J = 7.6, 1.3 Hz, 1H), 7.98−7.94 (m, 4H), 7.72 (t, J = 7.9 Hz, 1H), 7.54−7.52 (m, 2H), 7.50−7.47 (m, 4H); 13C NMR (151 MHz, CDCl3) δ 171.2, 148.9, 137.4, 137.3, 136.3, 132.6, 132.3 (d, J = 1.4 Hz), 131.8, 131.7 (d, J = 9.2 Hz), 130.3, 128.8 (d, J = 12.7 Hz), 127.7, 123.9; FT-IR 3075, 2924, 2854, 1622, 1528, 1350, 1211 818 cm−1; mp = 173 °C; HRMS (ESI-TOF) calcd for C19H15N2O3PNa [M + Na]+ 373.0718, found 373.0718. N-(2-Nitrobenzylidene)-P,P-diphenylphosphine amide (3g): light brown solid, 873 mg, overall yield 25%; 1H NMR (600 MHz, CDCl3) δ 9.62 (d, J = 30.6 Hz, 1H), 8.16 (dd, J = 7.7, 1.4 Hz, 1H), 8.01 (dd, J = 8.0, 1.1 Hz, 1H), 7.96−7.91 (m, 4H), 7.75 (dt, J = 7.5, 0.9 Hz, 1H), 7.70 (dt, J = 7.8, 1.5 Hz, 1H), 7.54−7.52 (m, 2H), 7.40−7.47 (m, 4H); 13 C NMR (151 MHz, CDCl3) δ 169.6, 149.9, 133.4, 133.2, 132.8, 132.4, 132.2 (d, J = 1.7 Hz), 131.8 (d, J = 9.3 Hz), 131.6, 130.8, 130.5, 130.3, 128.8 (d, J = 12.7 Hz), 124.6; FT-IR 3061, 2917, 1620, 1526, 1437, 1350, 1206, 1125, 820 cm−1; mp = 100 °C; HRMS (ESI-TOF) calcd for C19H15N2O3PNa [M + Na]+ 373.0718, found 373.0719. General Procedure for the Nitro-Mannich Reaction. In a typical procedure, Fe(OTf)2 (7.1 mg, 0.02 mmol) and TPS-he-pybox L7 (16 mg, 0,02 mmol) were dissolved in dry and deoxygenated THF (0.5 mL) under a argon atmosphere and stirred at room temperature for 30 min. Nitroalkane (0.214 mL, 4 mmol) was then added, and the deep-purple mixture was stirred for an additional 30 min. Then the corresponding N-phosphinoylimine (0.4 mmol) was added followed by TEA (0.28 mL, 0.2 mmol), and the reaction was stirred at room temperature for 2 h. After this time, the reaction mixture was directly poured onto a silica gel column and eluted by chloroform−acetone (10:1) to yield the desired adduct. (R)-(−)-N-(2-Nitro-1-phenylethyl)diphenylphosphine amide (2c):26 white solid, 122 mg, yield 83%; ee 96% by HPLC Chiralcel OD-H Hx/ 2-propanol (90:10), flow 1.0 mL/min; UV = 220 nm, 35 °C, tS = 17.8 min (minor) (S), tR = 31.7 min (major) (R); [α]D25 = −53.8 (c = 1.0, CHCl3) [lit.26 [α]D28 = +33.2 (for enantiomer S, c = 0.9, CHCl3)]; 1 H NMR (600 MHz, CDCl3) δ = 7.85−7.81 (m, 4H), 7.55−7.50 (m, 2H), 7.47−7.41 (m, 4H), 7.37−7.29 (m, 5H), 4.95−4.92 (m, 3H), 4.04−4.01 (m, 1H); 13C NMR (151 MHz, CDCl3): δ = 137.9 (d, J = 5.9 Hz), 132.6−132.4 (m), 132.3, 131.9, 131.8 (d, J = 9.8 Hz), 131.5, 130.8, 129.3, 128.9−128.7 (m), 126.4, 81.0, 55.4. (R)-(−)-N-(2-Nitro-1-(4-methylphenyl)ethyl)diphenylphosphine amide (4a): 26 white solid, 79 mg, yield 52%; ee 94% by HPLC Chiralcel OD-H Hx/2-propanol (90:10), flow 1.0 mL/min, UV = 220 nm, 21 °C, tS = 20.5 min (minor, S), tR = 28.9 min (major, R); [α]D25 = −63.6 (c = 1.0, CHCl3) [lit.26 [α]D30 = +87.3 (for enantiomer S, c = 1.12, CHCl3)]; 1H NMR (600 MHz, DMSO) δ = 7.70−7.63 (m, 4H), 7.57−7.48 (m, 4H), 7.44−7.41 (m, 2H), 7.21 (d, J = 8.1 Hz, 2H), 7.11(d, J = 7.8 Hz, 2H), 6.28 (dd, J = 11.1, 8.9 Hz 1H), 4.87 (dd, J = 12.3, 8.5 Hz, 1H), 4.80 (ddd, J = 12.3, 6.4, 1.0 Hz 1H), 4.67−4.61 (m, 1H), 2.27 (s, 3H); 13C NMR (151 MHz, DMSO) δ = 137.0, 136.6 11221

DOI: 10.1021/acs.joc.7b01786 J. Org. Chem. 2017, 82, 11218−11224

Note

The Journal of Organic Chemistry

(151 MHz, DMSO) δ 147.2, 134.6, 134.0, 133.2, 132.6, 132.3, 132.0−131.4 (m), 129.8, 129.3, 128.4 (dd, J = 20.8, 12.3 Hz), 124.3, 79.7 (d, J = 6.7 Hz), 48.7 (d, J = 7.8 Hz); FT-IR: 3139, 2914, 1550, 1525, 1348, 1179 cm−1; mp = 212 °C; HRMS (ESI-TOF) calcd for C20H18N3O5PNa [M + Na]+ 434.0882 found 434.0876. (R)-(−)-N-(1-(Furyl)-2-nitroethyl)diphenylphosphine amide (4h):26 light yellow solid, 110 mg, yield 77%; ee 90% by HPLC Chiralcel OD-H Hx/2-propanol (90:10), flow 1.0 mL/min, UV = 220 nm, 21 °C, tS = 9.1 min (minor, S), tR = 15.8 min (major, R); [α]D25 = −57.7 (c = 1.0, CHCl3) [lit.26 [α]D29 = +41.8 (for enantiomer S, c = 0.98, CHCl3)]; 1 H NMR (600 MHz, CDCl3) δ 7.91−7.88 (m, 2H), 7.84−7.80 (m, 2H), 7.56−7.52 (m, 2H), 7.48−7.44 (m 4H), 7.35 (dd, J = 1.8, 0.8 Hz, 1H), 6.33 (dd, J = 3.3, 1.8 Hz, 2H), 5.01−4.96 (m, 1H), 4.92−4.98 (m, 2H), 3.96 (dd, J = 10.7, 7.0 Hz, 1H); 13C NMR (151 MHz, CDCl3) δ 150.7 (d, J = 7.4 Hz), 143.0, 132.5 (m), 132.1, 131.8 (d, J = 9.9 Hz), 131.6, 131.3, 130.7, 129.0, 128.9 (t, J = 12.0 Hz), 110.9, 108.3, 78.5 (d, J = 2.3 Hz), 47.9. (R)-(−)-N-(1-(2-Naphthyl)-2-nitroethyl)diphenylphosphine amide (4i): 26 white solid, 120 mg, yield 72%; ee 98% by HPLC Chiralcel OD-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tS = 16.8 min (minor, S), tR = 22.4 min (major, R); [α]D25 = −97.3 (c = 1.0, CHCl3) [lit.26 [α]D30 = +56.6 (for enantiomer S, c = 0.47, MeOH)]; 1 H NMR (600 MHz, DMSO) δ 7.89−7.88 (m, 2H), 7.83−7.82 (m, 1H), 7.77 (s, 1H), 7.73−7.66 (m, 4H), 7.60 (dd, J = 8.6, 1.8 Hz, 2H), 7.53−7.47 (m, 5H), 7.40 (td, J = 7.6, 3.0 Hz, 2H), 6.46 (dd, J = 10.9, 9.1 Hz, 1H), 5.02−4.94 (m, 2H), 4.91−4.85 (m, 1H); 13C NMR (151 MHz, DMSO) δ 137.0 (d, J = 2.3 Hz), 133.7, 133.4, 132.9, 132.6−132.5 (m), 131.8−131.6 (m), 128.5−128.2 (m), 127.9, 127.5, 126.3 (d, J = 15.4 Hz), 125.8 (d, J = 3.9 Hz), 124.8, 80.8 (d, J = 6.5 Hz), 53.7. (R,E)-(−)-N-(1-Nitro-4-phenylbut-3-en-2-yl)diphenylphosphine amide (4j): 26 light cream solid, 116 mg, yield 74%; ee 96% by HPLC Chiralcel OD-H Hx/2-propanol (90:10), flow 1.0 mL/min, UV = 220 nm, 21 °C, tS = 20.5 min (minor, S), tR = 28.9 min (major, R); [α]D25 = −90.2 (c = 1.0, CHCl3) [lit.26 [α]D31 = +39.1 (for enantiomer S, c = 1.04, CHCl3)]; 1H NMR (600 MHz, CDCl3) δ 7.93−7.90 (m, 2H), 7.87−7.84 (m, 2H), 7.54−7.51 (m, 4H), 7.47−7.44 (m, 4H), 7.30 (d, J = 4.4 Hz, 2H), 7.27−7.25 (m, 1H), 6.60 (dd, J = 15.9, 1.4 Hz, 1H), 6.18 (dd, J = 15.9, 6.3 Hz, 1H), 4.79 (dd, J = 12.8, 5.1 Hz, 1H), 4.73 (dd, J = 12.8, 5.2 Hz, 1H), 4.45−4.38 (m, 1H), 3.92−3.87 (m, 1H); 13C NMR (151 MHz, CDCl3) δ 135.7, 133.6, 132.6, 132.5, 131.9 (d, J = 9.9 Hz), 131.6, 131.1, 129.5, 129.0−128.7 (m), 128.5, 126.9, 125.5 (d, J = 5.8 Hz), 80.6, 51.7. N-(2-Nitro-1-phenylpropyl)diphenylphosphine amide (4k): 26 white solid, 92 mg, yield 61%; ee1D = 88%, ee2D = 90% by HPLC Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, major diastereomer: t1 = 11.4 min (major), t2 = 24.7 min (minor), minor diastereomer: t1 = 20.8 min (major), t2 = 47.6 min (minor); 1H NMR (600 MHz, CDCl3) δ 7.82−7.76 (m, 2Hmajor, 2Hminor), 7.73−7.66 (m, 2Hmajor, 2Hminor), 7.55−7.41 (m, 4Hmajor, 4Hminor), 7.38−7.28 (m, 4Hmajor, 4Hminor), 7.15 (dd, J = 7.7, 1.5 Hz, 2H), 7.14−7.09 (m, 2H), 5.02−4.99 (m, 1Hmajor), 4.89 (qui, J = 6.8 Hz, 1Hminor), 4.56 (td, J = 11.1, 5.4 Hz, 1Hmajor), 4.50−4.46 (td, J = 10.5, 3.2 Hz, 1Hminor), 4.22 (dd, J = 11.4, 7.4 Hz, 1Hmajor), 4.17 (dd, J = 11.1, 7.2 Hz, 1Hminor), 1.54 (d, J = 6.8 Hz, 3Hmajor), 1.51 (d, J = 6.7 Hz, 3Hminor). 13C NMR (151 MHz, CDCl3) δ 138.6 (d, J = 1.6 Hz), 137.5 (d, J = 4.2 Hz), 132.7 (d, J = 9.8 Hz), 132.5−132.0 (m), 131.9−131.7 (m) 131.5, 131.4, 130.9, 129.1, 128.9−128.5 (m), 127.0, 126.8, 88.3 (d, J = 2.9 Hz), 87.6, 58.5, 58.4, 17.3, 15.6. N-(1-(4-Methoxyphenyl)-2-nitropropyl)diphenylphosphine amide (4l): 28 white solid, 64 mg, yield 40%; ee1D = 90%, ee2D = 89% by HPLC Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, major diastereomer: t1 = 13.2 min (major), t2 = 39.1 min (minor), minor diastereomer: t1 = 31.6 min (major), t2 = 77.3 min (minor); 1H NMR (600 MHz, CDCl3) δ 7.80−7.76 (m, 2Hmajor, 2Hminor), 7.71−7.69 (m, 2Hmajor, 2Hminor), 7.54−7.42 (m, 4Hmajor, 4Hminor), 7.39−7.31 (m, 2Hmajor, 2Hminor), 7.07−7.05 (m, 2Hminor), 7.03−7.01 (m, 2Hmajor) 6.84−6.81 (m, 2Hmajor, 2Hminor), 5.02−4.97 (m, 1Hmajor), 4.89−4.83 (m, 1Hminor), 4.50 (td, J = 11.1, 5.3 Hz, 1Hmajor), 4.43−4.41 (m, 1Hminor), 4.11 (dd, J = 11.3, 7.3 Hz, 1Hmajor), 4.01 (dd, J = 10.9, 6.7 Hz, 1Hminor), 3.79 (s, 3Hmajor, 3Hminor), 1.54

(d, J = 3.1 Hz), 133.7, 133.5, 132.8, 132.6, 131.8−131.6 (m), 129.0, 128.4 (t, J = 11.3 Hz), 126.7, 81.9 (d, J = 4.5 Hz), 53.3, 20.7. (R)-(−)-N-(1-(4-Methoxyphenyl)-2-nitroethyl)diphenylphosphine amide (4b): 27 white solid, 92 mg, yield 58%; ee 94% by HPLC Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tR = 28.1 min (major, R), tS = 49.8 min (minor, S); [α]D25 = −67.5 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3): δ = 7.85−7.80 (m, 4H), 7.54−7.50 (m, 2H), 7.46−7.41 (m, 4H), 7.22−7.19 (m, 2H), 6.88−6.85 (m, 2H), 4.91 (dd, J = 12.6, 6.0 Hz, 1H), 4.85 (dd, J = 12.6, 5.9 Hz, 1H), 4.82−4.78 (m, 1H), 3.79 (s, 3H); 13 C NMR (151 MHz, CDCl3) δ = 159.8, 132.6−132.5 (m), 131.9−131.8 (m), 131.6, 130.9, 129.9 (d, J = 6.1 Hz), 128.8 (dd, J = 12.7, 5.0 Hz), 127.7, 114.6, 81.0, 55.4 (d, J = 5.1 Hz), 53.0. (R)-(−)-N-(1-(4-Chlorophenyl)-2-nitroethyl)diphenylphosphine amide (4c): 26 white solid, 119 mg, yield 74%; ee 94% by HPLC Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tR = 15.6 min (major, R), tS = 23.8 min (minor, S); [α]D25 = −71.7 (c = 1.0, CHCl3) [lit.26 [α]D29 = +46.6 (for enantiomer S, c = 1.01, CHCl3)]; 1H NMR (600 MHz, CDCl3): δ = 7.82−7.78 (m, 4H), 7.55−7.50 (m, 2H), 7.47−7.40 (m, 4H), 7.32−7.30 (m, 2H), 7.25−7.22 (m, 2H), 4.90−4.78 (m, 3H), 4.17 (dd, J = 10.8, 6.2 Hz, 1H); 13C NMR (151 MHz, CDCl3) δ 136.5 (d, J = 5.5 Hz), 134.7, 132.6−132.4 (m), 132.1, 131.9 (d, J = 9.8 Hz), 131.6, 131.2, 130.8, 129.4, 128.9 (d, J = 12.7 Hz), 127.9, 80.7 (d, J = 1.7 Hz), 52.8. (R)-(−)-N-(1-(4-(Trifluoromethyl)phenyl)-2-nitroethyl)diphenylphosphine amide (4d): white solid, 149 mg, yield 84%; ee 94% by HPLC Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tR = 11.4 min (major, R), tS = 17.7 min (minor, S); [α]D25 = −55.8 (c = 1.0, CHCl3); 1H NMR (600 MHz, DMSO) δ 7.72−7.67 (m, 6H), 7.65−7.58 (m, 3H), 7.54−7.48 (m, 3H), 7.42 (dt, J = 7.6, 3.0 Hz, 2H), 6.48 (dd, J = 10.7, 9.2 Hz, 1H), 4.97−4.87 (m, 2H), 4.86−4.76 (m, 1H); 13C NMR (151 MHz, DMSO) δ 144.1, 133.5, 133.1, 132.7, 132.2, 131.9−131.6 (m), 128.7−128.3 (m), 127.9, 125.3, 125.1, 123.2, 80.3 (d, J = 6.1 Hz) 53.09; FT-IR: 3130, 2902, 1549, 1372, 1118 cm−1; mp = 175 °C; HRMS (ESI-TOF) calcd for C21H18F3N2O3PNa [M + Na]+ 457.0905, found 457.0909. (R)-(−)-N-(2-Nitro-1-(4-nitrophenyl)ethyl)diphenylphosphine amide (4e): light yellow solid, 122 mg, yield 74%; ee 96% by HPLC Chiralcel OD-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tR = 14.8 min (major, R), tS = 27.9. (minor, S); [α]D25 = −54.8 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3) δ 8.20−8.19 (m, 2H), 7.83−7.77 (m, 4H), 7.58−7.43 (m, 8H), 4.96−4.92 (m, 3H), 4.46−4.41 (m, 1H); 13C NMR (151 MHz, CDCl3) δ 148.0, 145.0 (d, J = 5.1 Hz), 132.8, 132.3 (d, J = 9.7 Hz), 131.9 (d, J = 9.8 Hz), 131.7, 131.4, 130.8, 130.6 129.1−128.9 (m), 127.7, 124.4, 80.4 (d, J = 3.0 Hz), 52.9; FT-IR 3107, 2906, 1552, 1519, 1347, 1179 cm−1; mp = 172 °C; HRMS (ESI-TOF) calcd for C20H18N3O5PNa [M + Na]+ 434.0882, found 434.0857. (R)-(−)-N-(2-Nitro-1-(3-nitrophenyl)ethyl)diphenylphosphine amide (4f): light yellow solid, 150 mg, yield 91%; ee 89% by HPLC Chiralcel OD-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tR = 15.2 min (major, R), tS = 20.2 min (minor, S); [α]D25 = −58.1 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3) δ = 7.79−7.84 (m, 4H), 7.60−7.62 (m, 2H), 7.48−7.57 (m, 2H), 7.40−7.43 (m, 6H), 4.87−4.92 (m, 3H), 4.22 (dd, J = 10.2, 6.2 1H); 13C NMR (151 MHz, CDCl3) δ = 141.9 (d, J = 5.4 Hz), 132.7, 132.4 (d, J = 9.7 Hz), 131.9 (d, J = 10.0 Hz), 131.5, 131.1 (d, J = 2.6 Hz), 130.8, 130.7, 129.0, 128.9 (d, J = 12.8 Hz), 127.0, 126.2 (d, J = 3.2 Hz), 124.8, 123.0, 80.6 (d, J = 2.5 Hz), 53.0; FT-IR 3138, 2912, 1552, 1529, 1349, 1178 cm−1; mp = 174 °C; HRMS (ESI-TOF) calcd for C20H18N3O5PNa [M + Na]+ 434.0882 found 434.0863. (R)-(−)-N-(2-Nitro-1-(2-nitrophenyl)ethyl)diphenylphosphine amide (4g): white solid, 97 mg, yield 61%; ee 97% by HPLC Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, tR = 12.8 min (major, R), tS = 21.6 min (minor, S); [α]D25 = −53.5 (c = 1.0, CHCl3); 1H NMR (600 MHz, DMSO) δ 8.04 (dd, J = 7.9, 0.9 Hz, 1H), 7.90 (dd, J = 8.2, 1.1 Hz, 1H), 7.79 (dt, J = 11.2, 1.0 Hz, 1H), 7.63−7.49 (m, 9H), 7.38 (dt, J = 7.7, 3.1 Hz, 2H), 6.66 (t, J = 10.1 Hz, 1H), 5.36 (ddd, J = 19.0, 10.1, 4.2 Hz, 1H), 4.92 (ddd, J = 12.6, 4.1, 2.2 Hz, 1H), 4.83 (dd, J = 12.7, 9.8 Hz, 1H); 13C NMR 11222

DOI: 10.1021/acs.joc.7b01786 J. Org. Chem. 2017, 82, 11218−11224

Note

The Journal of Organic Chemistry (d, J = 6.8 Hz,3Hmajor), 1.50 (d, J = 6.7 Hz, 3Hminor); 13C NMR (151 MHz, CDCl3) δ 159.7 (d, J = 8.7 Hz), 132.7 (d, J = 9.8 Hz), 132.6, 132.5−132.1 (m), 131.9−131.8 (m), 131.5, 131.4, 131.0, 130.6 (d, J = 2.1 Hz), 129.5 (d, J = 4.4 Hz), 128.8−128.5 (m), 128.2, 128.0, 114.5, 114.3, 88.5 (d, J = 5.9 Hz), 87.8, 58.1, 57.9, 55.4 (d, J = 6.4 Hz), 17.2 (d, J = 3.2 Hz), 15.8 (d, J = 3.0 Hz). N-(3-(tert-Butyldimethylsiloxy)-2-nitro-1-phenylpropyl)diphenylphosphine amide (4n): white solid, 35 mg, yield 50%; eemajor = 89%, by HPLC major diastereomer: Chiralcel OZ-H Hx/2-propanol (80:20), flow 1.0 mL/min, UV = 220 nm, 21 °C, t1 = 6.6 min (major), t2 = 9.5 min (minor); 1H NMR (600 MHz, CDCl3) δ 7.80−7.77 (m, 2H), 7.69−7.65 (m, 2H), 7.55−7.52 (m, 1H), 7.48−7.42 (m, 3H), 7.33−7.29 (m, 5H), 7.16−7.15 (m, 2H), 4.93−4.89 (m, 1H), 4.65−4.60 (m, 1H), 4.16−4.11 (m, 2H), 3.76 (dd, J = 7.7, 3.9 Hz, 1H), 0.79 (s, 9H), −0.03 (d, J = 8.0 Hz, 6H); 13C NMR (151 MHz, CDCl3) δ 138.3 (d, J = 1.9 Hz), 132.4−132.0 (m), 131.4 (d, J = 5.2 Hz), 129.2, 128.8−128.5 (m), 126.5, 94.2 (d, J = 5.5 Hz), 63.1, 55.0, 25.7, 18.1, −5.6 (d, J = 24.1 Hz); FT-IR 3147, 30.62, 2928, 2856, 1554, 1437, 1187, 1125 cm−1; mp = 159 °C; HRMS (ESI-TOF) calcd for C27H35N2O4PSiNa [M + Na]+ 533.2001, found 533.1996.

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(5) Palomo, C.; Oiarbide, M.; Halder, R.; Laso, A.; López, R. Angew. Chem., Int. Ed. 2006, 45, 117−120. (6) (a) Nugent, B. M.; Yoder, R. A.; Johnston, J. N. J. Am. Chem. Soc. 2004, 126, 3418−3419. (b) Davis, T. A.; Wilt, J. C.; Johnston, J. N. J. Am. Chem. Soc. 2010, 132, 2880−2882. (7) (a) Okino, T.; Nakamura, S.; Furukawa, T.; Takemoto, Y. Org. Lett. 2004, 6, 625−627. (b) Xu, X.; Furukawa, T.; Okino, T.; Miyabe, H.; Takemoto, Y. Chem. - Eur. J. 2006, 12, 466−476. (8) Hu, K.; Wang, C.; Ma, X.; Wang, Y.; Zhou, Z.; Tang, C. Tetrahedron: Asymmetry 2009, 20, 2178−2184. (9) Yoon, T. P.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2005, 44, 466−468. (10) (a) Fürstner, A. ACS Cent. Sci. 2016, 2, 778−789. For reviews on iron catalysis in organic synthesis, see: (b) Bolm, C.; Legros, J.; Le Paih, J.; Zani, L. Chem. Rev. 2004, 104, 6217−6254. (c) Sun, C.−L.; Li, B.−J; Shi, Z.−J. Chem. Rev. 2011, 111, 1293−1314. (d) Bauer, I.; Knölker, H.−J. Chem. Rev. 2015, 115, 3170−3387. For recent precedents on the use of iron salt in asymmetric catalysis, see: (e) Zhou, P.; Lin, L.; Chen, L.; Zhong, X.; Liu, X.; Feng, X. J. Am. Chem. Soc. 2017, 139, 13414. (f) Xu, H.; Li, Y.-P.; Cai, C.; Wang, G.P.; Zhu, S.-F.; Zhou, Q.-L. J. Am. Chem. Soc. 2017, 139, 7697. (g) Narute, S.; Pappo, D. Org. Lett. 2017, 19, 2917. (11) Jankowska, J.; Paradowska, J.; Rakiel, B.; Mlynarski, J. J. Org. Chem. 2007, 72, 2228−2231. (12) (a) Desimoni, G.; Faita, G.; Quadrelli, P. Chem. Rev. 2003, 103, 3119−3154. (b) Rasappan, R.; Laventine, D.; Reiser, O. Coord. Chem. Rev. 2008, 252, 702−714. (c) For a comprehensive review about iron salts used with bis-oxazoline ligands, see: Ollevier, T. Catal. Sci. Technol. 2016, 6, 41. (13) For the application of pybox ligands in aldol reaction, see: (a) Evans, D. A.; Murry, J. A.; Kozlowski, M. C. J. Am. Chem. Soc. 1996, 118, 5814−5815. (b) Kobayashi, S.; Nagayama, S.; Busujima, T. Tetrahedron 1999, 55, 8739−8746. (c) Reichel, F.; Fang, X.; Yao, S.; Ricci, M.; Jørgensen, K. A. Chem. Commun. 1999, 1505−1506. (d) Evans, D. A.; Masse, C. E.; Wu, J. Org. Lett. 2002, 4, 3375−3378. (e) Desimoni, G.; Faita, G.; Piccinini, F.; Toscanini, M. Eur. J. Org. Chem. 2006, 2006, 5228−5230. (f) Zhao, J.−F.; Tan, B.−H.; Loh, T.− P. Chem. Sci. 2011, 2, 349−352. (g) Woyciechowska, M.; Forcher, G.; Buda, S.; Mlynarski, J. Chem. Commun. 2012, 48, 11029−11031. (14) For the application of pybox ligands in cyclopropanation, see: (a) Park, S.−B.; Murata, K.; Matsumoto, H.; Nishiyama, H. Tetrahedron: Asymmetry 1995, 6, 2487−2949. (b) Nishiyama, H.; Itoh, Y.; Sugawara, Y.; Matsumoto, H.; Aoki, K.; Itoh, K. Bull. Chem. Soc. Jpn. 1995, 68, 1247−1262. (c) Iwasa, S.; Tsushima, S.; Nishiyama, K.; Tsuchiya, Y.; Takezawa, F.; Nishiyama, H. Tetrahedron: Asymmetry 2003, 14, 855−865. (15) For the application of pybox ligands in Diels−Alder reaction, see: (a) Evans, D. A.; Barnes, D. M.; Johnson, J. S.; Lectka, T.; von Matt, P.; Miller, S. J.; Murry, J. A.; Norcross, R. D.; Shaughnessy, E. A.; Campos, K. R. J. Am. Chem. Soc. 1999, 121, 7582−7594. (b) Usuda, H.; Kuramochi, A.; Kanai, M.; Shibasaki, M. Org. Lett. 2004, 6, 4387− 4390. (c) Desimoni, G.; Faita, G.; Mella, M.; Piccinini, F.; Toscanini, M. Eur. J. Org. Chem. 2007, 2007, 1529−1534. (d) Shimizu, Y.; Shi, S.−L.; Usuda, H.; Kanai, M.; Shibasaki, M. Angew. Chem., Int. Ed. 2010, 49, 1103−1106. (16) For the application of pybox ligands in asymmetric reduction, see: (a) Nishiyama, H.; Kondo, M.; Nakamura, T.; Itoh, K. Organometallics 1991, 10, 500−608. (b) Nishiyama, N. H.; Yamaguchi, S.; Kondo, M.; Itoh, K. J. Org. Chem. 1992, 57, 4306− 4309. (c) Iovel, I.; Rubina, K.; Popelis, Y.; Gaukhman, A.; Lukevics, E. Chem. Heterocycl. Compd. 1996, 32, 294−307. (d) Bandini, M.; Cozzi, P. G.; Monari, M.; Perciaccante, R.; Selva, S.; Umani-Ronchi, A. Chem. Commun. 2001, 1318−1319. (e) Hosokawa; Ito, J.−i.; Nishiyama, H. Organometallics 2010, 29, 5773−5775. (f) Junge, K.; Möller, K.; Wendt, B.; Das, S.; Gördes, D.; Thurow, K.; Beller, M. Chem. - Asian J. 2012, 7, 314−320. (g) Łowicki, D.; Bezłada, A.; Mlynarski, J. Adv. Synth. Catal. 2014, 356, 591−595. (17) Iwasa, S.; Nakamura, H.; Nishiyama, H. Heterocycles 2000, 52, 939−944.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01786. NMR spectra and HPLC data (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jacek Mlynarski: 0000-0002-1794-306X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Polish National Science Centre (Grant No. NCN 2012/07/B/ST5/00909) is gratefully acknowledged.

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REFERENCES

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