Method for Catalytic Enantioselective Alkylation of Aldehydes Using

May 10, 2018 - Alkyltitanium reagents, generated in situ from Grignard reagents and ClTi(OiPr)3, can be employed without further manipulation in the ...
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Article Cite This: J. Org. Chem. 2018, 83, 6127−6132

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Method for Catalytic Enantioselective Alkylation of Aldehydes Using Grignard Reagents as Alkyl Sources Kento Tanaka, Munehisa Tomihama, Koji Yamamoto, Naoki Matsubara, and Toshiro Harada* Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan S Supporting Information *

ABSTRACT: Alkyltitanium reagents, generated in situ from Grignard reagents and ClTi(OiPr)3, can be employed without further manipulation in the enantioselective alkylation of aldehyde by the catalysis of a chiral titanium complex derived from DTBP-H8-BINOL. The reaction is performed with good stoichiometry [1.5 equiv each of Grignard reagents and ClTi(OiPr)3] at a low catalyst loading (2 mol %), affording a variety of chiral secondary alcohols in high enantioselectivity and yields and, hence, realizing an asymmetric version of the Grignard reaction in an indirect manner.

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INTRODUCTION The catalytic enantioselective addition of organometallic reagents to aldehydes and ketones is one of the most useful methods for the synthesis of chiral alcohols with simultaneous C−C bond formation.1−8 Although the recent development of efficient catalytic systems has extended the scope of organometallic reagents that can be applied to this reaction, the use of Grignard reagents has been relatively less exploited.9−21 The preparation of Grignard reagents is well-established. A variety of reagents are commercially available and commonly used both in the laboratory and in industry. Accordingly, an asymmetric version of the Grignard reaction that enables the enantioselective preparation of chiral secondary and tertiary alcohols has been of considerable interest for a long time.22,23 However, the use of Grignard reagents in catalytic enantioselective addition is difficult because to their high activity that concurrently induces noncatalytic racemic reaction. Recently, Harutyunyan and Minnaard have shown for the first time that the enantioselective addition of alkyl Grignard reagents to ketones can be realized by chiral Cu(I) catalysts.24−28 Despite such advancement, the enantioselective addition to the significantly more reactive aldehydes remains a challenging problem. For aldehydes, indirect methods in which Grignard reagents are used after conversion to organotitanium and -zinc reagents have been developed. Seebach reported TADDOLate-Ticatalyzed enantioselective alkylation of aldehydes with alkyltitanium reagents RTi(OiPr)3, generated from RMgBr by transmetalation with ClTi(OiPr)3.10 The rigorous exclusion of co-produced magnesium salts is necessary to achieve high enantioselectivity, requiring complexation with 1,4-dioxane and centrifugation of the resulting precipitate. In the enantioselective addition to aldehydes catalyzed with a chiral amino alcohol, diorganozinc reagents generated from Grignard reagents by transmetalation with Zn(OMe)2 were successfully employed by Charette after the removal of precipitated magnesium salts via centrifugation.11 We have recently reported a synthetically © 2018 American Chemical Society

simples method in which Grignard reagents are used as a mixed reagent with excess Ti(OiPr)4 without further manipulation.13−16 By virtue of the enhanced activity of chiral titanium catalysts derived from BINOL derivatives 1b and 2b bearing a sterically demanding aryl group at position 3,29,30 the in situgenerated mixed reagents undergo highly enantioselective alkylation and arylation of aldehydes even at 2 mol % catalyst loading. As a typical reaction protocol, 1.2 equiv of Grignard reagents and 3 equiv of Ti(OiPr)4 are used for the enantioselective arylation. On the other hand, for the alkylation, a further excess of Grignard reagents (2.2 equiv) and the titanium alkoxide (5.8 equiv) are employed. Although Ti(OiPr)4 is a nontoxic, lowcost chemical, a decrease in the amount is desirable to improve practicality. Da et al. reported that the amount of Ti(OiPr)4 can be decreased to 0.9−1.4 equiv by the use of alkyl Grignard reagents (2 equiv) with bis[2-(N,N′-dimethylamino)ethyl]ether as a chelating additive, albeit at a higher loading of the parent BINOL 1a (15 mol %).17,18

In this study, we examine the use of alkyltitanium reagents, generated in situ from Grignard reagents and ClTi(OiPr)3, in the alkylation of aldehydes with a titanium catalyst derived from DTBP-H8-BINOL [(R)-2c] (Scheme 1). We report herein the result of this study that demonstrates that (1) 1.5 equiv each of Grignard reagents and the titanium alkoxide is sufficient, (2) the resulting titanium reagents can be used directly without Received: April 12, 2018 Published: May 10, 2018 6127

DOI: 10.1021/acs.joc.8b00929 J. Org. Chem. 2018, 83, 6127−6132

Article

The Journal of Organic Chemistry

10 mol % catalyst loading, the ligand exhibited inferior results (72% yield, 92% ee).31 The butyltitanium reagent is moderately reactive, affording racemic 3a in 27% yield in the absence of the chiral ligands. These results imply a high activity of the chiral titanium catalyst derived from (R)-2c that overrides the background racemic reaction of the titanium reagent. The results of our enantioselective alkylation reaction with a variety of aldehydes and Grignard reagents are summarized in Table 1. Not only aromatic aldehydes but also a heteroaromatic aldehyde (entries 19−22) and α,β-unsaturated aldehydes (entries 23 and 24) underwent enantioselective alkylation under the optimized conditions to give product alcohols 3 in high yields and ee’s (85−98%). The reaction of an aliphatic aldehyde however resulted in poor conversion and selectivity (entry 25).

Scheme 1. Catalytic Enantioselective Alkylation of Aldehydes Using Grignard Reagents

centrifugation, and (3) a variety of chiral secondary alcohols are obtained in high yields and enantioselectivities at a 2 mol % catalyst loading.

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RESULTS AND DISCUSSION BuMgCl (1.5 equiv, 2 M in Et2O) was treated with ClTi(OiPr)3 (1.5 equiv) in the presence of Ti(OiPr)4 (0.3 equiv) at −78 °C in Et2O to give a mixture of BuTi(OiPr)3 and MgCl2 (Scheme 2). Scheme 2. Catalytic Enantioselective Butylation of 1-Naphthaldehyde Using BuMgCl

The halogen atom of Grignard reagents could also be bromine as demonstrated in the reaction employing BuMgBr (entries 3 and 20) and n-C6H13MgBr (entries 8 and 22). In general, reactions using primary alkyl Grignard reagents proceeded efficiently (entries 1−3, 6−9, and 14−25). Despite high selectivity, product yields were moderate for the reaction using EtMgCl (entry 4) and iBuMgCl (entry 10). In the former reaction, the pinacol coupling of 1-naphthaldehyde concurrently proceeded to give [1-naphCH(OH)]2 as a byproduct (14%), suggesting the generation of Ti(III) species by the decomposition of the ethyltitanium reagents in the first step of the reaction.32 An improved yield was obtained when 2 equiv of the titanium reagent was employed (entry 5). In the later reaction, on the other hand, formation of the pinacol-coupling product was not observed, implying that the isobutyltitanium reagent is stable31 but less reactive probably for steric reasons. The longer reaction time resulted in decreased selectivity, albeit with improvement in the product yield (entry 11). The reaction of secondary cyclohexyl Grignard reagents was very sluggish under the optimized conditions. However, becuase the reaction was performed at room temperature for 18 h at higher concentrations, the corresponding alkylation product was obtained in 52% yield and 91% ee (entry 12).33 The reaction of PhMgBr was moderately selective, although the product yield was high (entry 13). The preparative utility of the reaction presented here is demonstrated in a gram-scale synthesis of alcohol (R)-3a (entry 2). Even with 96 mg (2 mol %) of chiral ligand (R)-2c, the reaction of 1-naphthaldehyde (9.9 mmol) and BuMgCl (15 mmol) provided 1.80 g (85% yield) of the alcohol in 97% ee after isolation by vacuum distillation. The ligand was recovered from the residue for reuse in 88% yield.

The titanium reagent was transferred to a syringe together with the suspended magnesium salts as a fine powder, added to a Et2O solution of 1-naphthaldehyde (1 mmol), (R)-2c (2 mol %), and 1,4-dioxane (1.5 equiv) at 0 °C for 1 h, and stirred for a further 0.5 h. Under these optimized conditions, (R)-alcohol 3a was obtained in 87% yield and 95% ee. In the first step of generating the butyltitanium reagent, Ti(OiPr)4 (0.3 equiv) is recommended as an additive to obtain reproducible yields. Otherwise, yields varied from 74 to 100%. An excess of BuMgCl with respect to ClTi(OiPr)3 induced considerable decomposition of the reagent. For example, the reaction using a reagent prepared from BuMgCl (2.1 equiv) and ClTi(OiPr)3 (1.5 equiv) gave 3a in only 10% yield. It is often difficult to adjust the mixing ratio to exactly 1:1. Ti(OiPr)4 as an additive ensures the absence of the excess Grignard reagent. The enantioselectivity of 3a was not increased further when a filtered solution of the butyltitanium reagent was employed (95% ee, 67% yield). On the other hand, the selectivity was decreased to some extent when the reaction was performed in the absence of 1,4-dioxane, which is known to form an insoluble complex with MgCl2 (89% ee, 95% yield). We speculate that the precipitated magnesium salt does not decrease the enantioselectivity of the reaction, whereas a small amount of the salt in the solution promotes the background racemic reaction pathway as a Lewis acid. The use of the parent ligand (R)-2a (2 mol %) resulted in lower conversion and selectivity (40% yield, 47% ee). Even at a

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CONCLUSION We have developed a practical method for the enantioselective alkylation of aldehydes using Grignard reagents as the alkyl group 6128

DOI: 10.1021/acs.joc.8b00929 J. Org. Chem. 2018, 83, 6127−6132

Article

The Journal of Organic Chemistry

7.81 mmol) in CH2Cl2 at −15 °C was added dropwise a solution of bromine (0.20 mL, 3.9 mmol) in CH2Cl2 for 1 h. Immediately after the addition, the reaction mixture was poured into water. An organic layer was separated and washed with aqueous Na2S2O3 (5%, 50 mL), dried (MgSO4), and concentrated in vacuo. The residue was purified by silica gel flash chromatography (5% ethyl acetate in toluene) to give 0.918 g (63% yield based on bromine) of the bromide as a light yellow powder: [α]D25 + 74.1 (c 1.3, CHCl3); 1H NMR (500 MHz, CDCl3) δ 1.62−1.77 (8H, m), 2.07−2.17 (2H, m), 2.23−2.36 (2H, m), 2.73−2.77 (4H, m), 4.39 (1H, s), 5.11 (1H, s), 6.81 (1H, d, J = 8.3 Hz), 7.06 (1H, d, J = 8.4 Hz), 7.31 (1H, s); 13C NMR (125 MHz, CDCl3) δ 22.68, 22.74, 22.9, 23.0, 26.9, 27.1, 29.0, 29.2, 107.0, 112.9, 119.8, 120.9, 130.0, 130.9, 131.8, 133.2, 136.5, 137.3, 148.0, 150.7; HRMS (FAB double focusing) calcd for C20H21O279Br M+ 372.0725, found 372.0727. (R)-3-(3,5-Di-tert-butylphenyl)-2,2′-dihydroxy5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl [(R)-2c]. A mixture of 3,5-di-tert-butylphenylboronic acid (0.351 g, 1.50 mmol),35 (R)-3bromo-2,2′-dihydroxy-5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl (0.374 g, 1.00 mmol), and K2CO3 (0.218 g, 1.50 mmol) in DME (6 mL) was degassed through a freeze−pump−thaw cycle (three times). To this under an argon atmosphere were added Pd(OAc)2 (11 mg, 0.050 mmol, 5 mol %) and di(1-adamantyl)butylphosphine (22 mg, 0.060 mmol, 6 mol %). The resulting gray suspension was heated under reflux for 21 h. Aqueous saturated NH4Cl (15 mL) was added. The mixture was extracted with ethyl acetate (2 × 50 mL), washed with brine, dried (Na2SO4), and concentrated in vacuo. The residue was purified by silica gel flash chromatography (10% ethyl acetate in hexane) to give 0.406 g (84% yield) of (R)-2c as a light yellow powder: [α]D23 + 63.3 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) δ 1.36 (18H, s), 1.64−1.82 (8H, m), 2.17−2.29 (2H, m), 2.31−2.45 (2H, m), 2.73−2.85 (4H, m), 4.65 (1H, br), 4.97 (1H, br), 6.85 (1H, d, J = 8.3 Hz), 7.07 (1H, d, J = 8.3 Hz), 7.14 (1H, s), 7.38 (2H, d, J = 1.8 Hz), 7.40 (1H, t, J = 1.8 Hz); 13 C NMR (125 MHz, CDCl3) δ 22.98, 23.04, 23.06, 23.09, 27.1, 27.2, 29.26, 29.27, 31.5, 34.9, 112.8, 119.6, 120.1, 121.4, 123.5, 127.1, 129.9, 130.1, 130.7, 131.7, 136.5, 136.7, 136.9, 148.3, 150.9, 151.0; HRMS (FAB double focusing) calcd for C34H42O2 M+ 482.3185, found 482.3177. n-C6H13MgCl Solution in Cyclopentyl Methyl Ether and Et2O. Magnesium turnings (2.40 g, 100 mmol) were placed in a reaction flask, heated under vacuum at 170 °C for 0.5 h, and suspended in cyclopentyl methyl ether (5 mL) under an argon atmosphere. To this was added a 2 mL portion of a solution of 1-chlorohexane (6.0 g, 50 mmol) in cyclopentyl methyl ether (13 mL), and the mixture was heated at 90 °C while being stirred to start the reaction. After the initial exothermic reaction had ceased, the rest of the solution was added dropwise to the reaction mixture at 90 °C for 1.5 h. After being stirred for 1 h under gentle refluxing, the resulting suspension was diluted with Et2O (25 mL) and filtered through Celite to give an n-C6H13MgCl solution. The concentration of the Grignard reagent was determined to be 0.85 M by titration using salicylaldehyde phenylhydrazone as an indicator.36 n-C5H11MgCl (0.81 M) and PhCH2CH2Mg (0.96 M) were prepared by a procedure similar to that described above. Typical Procedure for Catalytic Enantioselective Alkylation of Aldehydes Using Grignard Reagents. (R)-1-Naphthalen-1ylpentan-1-ol [(R)-3a]37 (Table 1, entry 1). Under an argon atmosphere, ClTi(OiPr)3 (0.5 M in Et2O, 3.0 mL, 1.5 mmol) was diluted with dry Et2O (13 mL) and Ti(OiPr)4 (0.088 mL, 0.3 mmol) was added. To this solution at −78 °C was added BuMgCl (2 M in Et2O, 0.75 mL, 1.5 mmol). The mixture was stirred at −78 °C for 15 min and then at 0 °C for 10 min. The resulting suspension was added with a syringe pump for 1 h to an Et2O (4 mL) solution of ligand 2c (9.6 mg, 0.020 mmol), 1,4-dioxane (0.13 mL, 1.5 mmol), and 1-naphthaldehyde (156 mg, 1.0 mmol) at 0 °C. After the mixture had been stirred at 0 °C for an additional 0.5 h, the reaction was quenched by the addition of aqueous 1 N HCl and the mixture extracted three times with ethyl acetate. The organic layers were washed successively with aqueous 5% NaHCO3 and brine, dried (Na2SO4), and concentrated in vacuo. The residue was purified by silica gel flash chromatography (5−30% ethyl acetate in hexane) to give 186 mg (87% yield) of (R)-3a (95% ee):38 1 H NMR (500 MHz, CDCl3) δ 0.91 (3H, t, J = 7.2 Hz), 1.32−1.60

Table 1. Catalytic Enantioselective Alkylation of Aldehydes Using Grignard Reagentsa entry 1 2b 3 4 5c 6 7 8 9 10d 11e,f 12f 13d 14 15 16 17 18 19c 20 21 22 23 24g 25

aldehyde

RMgX

1-naphCHO 1-naphCHO 1-naphCHO 1-naphCHO

BuMgCl BuMgCl BuMgBr EtMgCl

1-naphCHO 1-naphCHO 1-naphCHO 1-naphCHO 1-naphCHO

n-C5H11MgCl n-C6H13MgCl n-C6H13MgBr PhCH2CH2MgCl i BuMgCl

1-naphCHO 1-naphCHO PhCHO PhCHO p-ClC6H4CHO m-MeOC6H4CHO o-ClC6H4CHO 2-thieylCHO 2-thieylCHO 2-thieylCHO 2-thieylCHO PhCHCHCHO CH2C(Me)CHO PhCH2CH2CHO

CyMgCl PhMgBr BuMgCl PrMgCl n-C5H11MgCl PrMgCl BuMgCl BuMgCl BuMgBr n-C6H11MgCl n-C6H11MgBr BuMgCl BuMgCl BuMgCl

product

yield (%)

ee (%)

3a 3a 3a 3b 3b 3c 3d 3d 3e 3f 3f 3g 3h 4a 4b 4c 4d 4e 5a 5a 5b 5b 6a 6b 7

87 85 76 62 70 72 98 92 72 35 61 52 97 80 79 76 95 79 82 73 79 70 82 59 16

95 97 97 95 95 93 96 95 96 98 91 91 78 95 98 96 97 85 96 92 94 94 91 93 61

a

Unless otherwise noted, reactions were performed at a 1 mmol scale under the conditions shown in Scheme 2. bThe reaction was performed at a 9.9 mmol scale. cThe titanium reagent was prepared from EtMgCl (2 equiv), ClTi(OiPr)4 (2 equiv), and Ti(OiPr)4 (0.4 equiv). dTi(OiPr)4 was not used. eThe reaction was performed at 0 °C for 18 h after the addition of the titanium reagents over 5 min. f The reaction was performed at room temperature at a higher concentration for 18 h after the addition of the titanium reagents over 5 min. See the Experimental Section for details. gThe reaction was performed at a 2 mmol scale.

sources. It has been demonstrated that the high activity of a chiral titanium catalyst derived from DTBP-H8-BINOL (R)-2c enables the enantioselective addition of the in situ-generated alkyltitanium species from the Grignard reagents and ClTi(OiPr)3 without removal of co-produced magnesium salts. The reaction is performed with good stoichiometry at a low catalyst loading (2 mol %), affording a variety of chiral secondary alcohols in high enantioselectivities and yields.

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EXPERIMENTAL SECTION

General. Et2O, 1,4-dioxane, and cyclopentyl methyl ether were distilled from sodium benzophenone ketyl prior to use. Ti(OiPr)4 and TiCl4 were purchased from Wako Pure Chemical Industries, Ltd., and used as received. A stock solution of ClTi(OiPr)3 in Et2O (0.5 M) was prepared by mixing Ti(OiPr)4 and TiCl4 in a molar ratio of 3:1 in Et2O. BuMgCl (2 M in Et2O), PrMgCl (2 M in Et2O), EtMgCl (2 M in Et2O), i BuMgCl (2 M in Et2O), CyMgCl (2 M in Et2O), and PhMgBr (3 M in Et2O) were purchased from Sigma-Aldrich and used without titration. 1 H NMR and 13C NMR spectra were recorded on a Bruker Avance III spectrometer at 500 and 125 MHz, respectively. HRMS analyses were performed with a JEOL JMS-700 instrument in FAB double-focusing mode. Flash chromatography was performed with silica gel C-300 of Wako Pure Chemical Industries, Ltd. (R)-3-Bromo-2,2′-dihydroxy-5,5′,6,6′,7,7′,8,8′-octahydro1,1′-binaphthyl.34 To a solution of (R)-H8-BINOL (2.30 g, 6129

DOI: 10.1021/acs.joc.8b00929 J. Org. Chem. 2018, 83, 6127−6132

Article

The Journal of Organic Chemistry (4H, m), 1.78 (1H, br), 1.96−2.01 (2H, m), 5.48 (1H, dd, J = 4.8 and 7.9 Hz), 7.46−7.54 (3H, m), 7.64 (1H, d, J = 7.1 Hz), 7.78 (1H, d, J = 8.2 Hz), 7.87 (1H, d, J = 9.5 Hz), 8.13 (1H, d, J = 8.4 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1.0 mL/min, 4% iPrOH in hexane), giving retention times of 13.8 min (minor S enantiomer) and 29.4 min (major R enantiomer). The retention times were concordant with published values.39 The reaction described above was performed on a 9.92 mmol scale by following the same procedure except that a dropping funnel was used for the addition of the titanium reagent (Table 1, entry 2). Kugelrohr distillation (130−140 °C/5 mmHg) of the crude products gave 1.803 g (85% yield) of (R)-3a (97% ee). Flash chromatography (silica gel, 5% ethyl acetate in hexane) of the residue gave 84.8 mg (88% recovery) of ligand 2c. (R)-1-Naphthalen-1-ylpropan-1-ol (3b)40 (Table 1, entry 5). Yield 130 mg, 70%; 1H NMR (500 MHz, CDCl3) δ 1.04 (3H, t, J = 7.4 Hz), 1.82 (1H, br), 1.88−2.18 (2H, m), 5.41 (1H, dd, J = 5.0 and 7.6 Hz), 7.46−7.54 (3H, m), 7.64 (1H, d, J = 7.1 Hz), 7.78 (1H, d, J = 8.2 Hz), 7.88 (1H, d, J = 9.5 Hz), 8.12 (1H, d, J = 8.3 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1.0 mL/min, 10% iPrOH in hexane), giving retention times of 8.7 min (minor S enantiomer) and 15.6 min (major R enantiomer). The retention times were concordant with published values.41 (R)-1-Naphthalen-1-ylhexan-1-ol (3c)17 (Table 1, entry 6). Yield 165 mg, 72%; 1H NMR (500 MHz, CDCl3) δ 0.88 (3H, t, J = 6.9 Hz), 1.28−1.63 (6H, m), 1.9 (1H, br), 1.87−2.01 (2H, m), 5.48 (1H, dd, J = 4.8 and 8.0 Hz), 7.46−7.54 (3H, m), 7.65 (1H, d, J = 7.1 Hz), 7.78 (1H, d, J = 8.2 Hz), 7.88 (1H, d, J = 9.5 Hz), 8.13 (1H, d, J = 8.4 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1.0 mL/min, 10% iPrOH in hexane), giving retention times of 7.1 min (minor S enantiomer) and 13.6 min (major R enantiomer). The retention times were concordant with published values.17 (R)-1-Naphthalen-1-ylheptan-1-ol (3d)42 (Table 1, entry 7). Yield 236 mg, 98%; 1H NMR (500 MHz, CDCl3) δ 0.87 (3H, t, J = 6.8 Hz), 1.24−1.60 (8H, m), 1.76 (1H, br), 1.88−2.00 (2H, m), 5.48 (1H, dd, J = 4.8 and 7.9 Hz), 7.47−7.54 (3H, m), 7.65 (1H, d, J = 7.1 Hz), 7.78 (1H, d, J = 8.2 Hz), 7.88 (1H, d, J = 7.7 Hz), 8.13 (1H, d, J = 8.4 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 4% iPrOH in hexane), giving retention times of 12.6 min (minor S enantiomer) and 26.0 min (major R enantiomer). The retention times were concordant with published values.42 (R)-1-Naphthalen-1-yl-3-phenylpropan-1-ol (3e)18 (Table 1, entry 9). Yield 189 mg, 72%; 1H NMR (500 MHz, CDCl3) δ 1.57 (1H, br), 2.20−2.28 (2H, m), 2.81−2.93 (2H, m), 5.48 (1H, dd, J = 4.8 and 7.9 Hz), 7.18−7.26 (3H, m), 7.28−7.32 (2H, m), 7.46−7.51 (3H, m), 7.68 (1H, d, J = 7.2 Hz), 7.78 (1H, d, J = 8.3 Hz), 7.87 (1H, n), 7.93 (1H, m). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 10% iPrOH in hexane), giving retention times of 14.7 min (minor S enantiomer) and 26.3 min (major R enantiomer). The retention times were concordant with published values.18 (R)-3-Methyl-1-(naphthalen-1-yl)butan-1-ol (3f)17 (Table 1, entry 10). Yield 75 mg, 35%; 1H NMR (500 MHz, CDCl3) δ 1.01 (3H, d, J = 7.8 Hz), 1.12 (3H, d, J = 7.8 Hz), 1.73 (1H, m), 1.83 (1H, m), 1.97 (1H, m), 2.07 (1H, br), 5.54 (1H, dd, J = 3.8 and 9.4 Hz), 7.46−7.56 (3H, m), 7.66 (1H, d, J = 7.1 Hz), 7.78 (1H, d, J = 8.2 Hz), 7.89 (1H, d, J = 8.7 Hz), 8.11 (1H, d, J = 8.2 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 9% i PrOH in hexane), giving retention times of 7.62 min (minor S enantiomer) and 13.4 min (major R enantiomer). The retention times were concordant with published values.17 (R)-Cyclohexyl(naphthalen-1-yl)methanol (3g)31 (Table 1, entry 12). To a solution of ligand 2c (9.6 mg, 0.020 mmol) and dry Et2O (0.25 mL) under an argon atmosphere at room temperature was added ClTi(OiPr)3 (0.5 M in Et2O, 3.0 mL, 1.5 mmol). To the resulting solution at −78 °C was added CyMgCl (2 M in Et2O, 0.75 mL, 1.5 mmol). The mixture was stirred at −78 °C for 15 min and then at room temperature for 10 min. To the resulting suspension were added

1.4-dioxane (0.13 mL, 1.5 mmol) and 1-naphthaldehyde (156 mg, 1.0 mmol). After the mixture had been stirred at room temperature for 17 h, the reaction was quenched by the addition of aqueous 1 N HCl and the mixture extracted three times with ethyl acetate. The organic layers were washed successively with aqueous 5% NaHCO3 and brine, dried (Na2SO4), and concentrated in vacuo. The residue was purified by silica gel flash chromatography (5−30% ethyl acetate in hexane) to 125 mg (52% yield) of (R)-3g (91% ee): 1H NMR (500 MHz, CDCl3) δ 1.1− 1.24 (5H, m), 1.41 (1H, m), 1.60−2.00 (6H, m), 5.20 (1H, d, J = 6.5 Hz), 7.46−7.53 (3H, m), 7.58 (1H, d, J = 7.1 Hz), 7.78 (1H, d, J = 8.2 Hz), 7.87 (1H, d, J = 8.7 Hz), 8.15 (1H, d, J = 8.1 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OJ-H column (1 mL/min, 5% iPrOH in hexane), giving retention times of 8.5 min (minor S enantiomer) and 12.0 min (major R enantiomer). The retention times were concordant with published values.31 (R)-Naphthalen-1-ylphenylmethanol (3h)43 (Table 1, entry 13). Yield 228 mg, 97%; 1H NMR (500 MHz, CDCl3) δ 1.75 (1H, br), 6.55 (1H, s), 7.28 (1H, m), 7.34 (2H, m), 7.41−7.51 (5H, m), 7.64 (1H, d, J = 7.1 Hz), 7.82 (1H, d, J = 8.3 Hz), 7.87 (1H, m), 8.05 (1H, d, J = 9.2 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 10% iPrOH in hexane), giving retention times of 15.5 min (minor S enantiomer) and 33.1 min (major R enantiomer). The retention times were concordant with published values.43 (R)-1-Phenylpentan-1-ol (4a)40 (Table 1, entry 14). Yield 132 mg, 80%; 1H NMR (500 MHz, CDCl3) δ 0.88 (3H, t, J = 7.2 Hz), 1.20−1.45 (4H, m), 1.68−1.77 (2H, m), 1.78−1.87 (1H, m), 4.67 (1H, dd, J = 5.6 and 7.5 Hz), 7.26−7.30 (2H, m), 7.34−7.36 (3H, m). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (0.8 mL/min, 2% iPrOH in hexane), giving retention times of 17.0 min (major R enantiomer) and 18.3 min (minor S enantiomer). The retention times were concordant with published values.40 (R)-1-Phenylbutan-1-ol (4b)45 (Table 1, entry 15). Yield 119 mg, 79%; 1H NMR (500 MHz, CDCl3) δ 0.93 (3H, t, J = 7.4 Hz), 1.32 (1H, m), 1.43 (1H, m), 1.62−1.83 (3H, m), 4.68 (1H, dd, J = 5.9 and 7.6 Hz), 7.28 (2H, m), 7.34−7.36 (3H, m). Enantioselectivity was determined by HPLC analysis using a Chiralcel OB-H column (0.5 mL/min, 3% iPrOH in hexane), giving retention times of 16.6 min (minor S enantiomer) and 19.8 min (major R enantiomer). The retention times were concordant with published values.46 (R)-1-(4-Chlorophenyl)hexan-1-ol (4c)47 (Table 1, entry 16). Yield 161 mg, 76%; 1H NMR (500 MHz, CDCl3) δ 0.87 (3H, t, J = 7.1 Hz), 1.21−1.44 (6H, m), 1.55−1.80 (3H, m), 4.65 (1H, dd, J = 5.9 and 7.4 Hz), 7.27−7.33 (4H, m). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 0.5% i PrOH in hexane), giving retention times of 30.5 min (minor S enantiomer) and 34.0 min (major R enantiomer). The absolute stereochemistry was assumed by analogy. (R)-1-(3-Methoxyphenyl)butan-1-ol (4d)48 (Table 1, entry 17). Yield 171 mg, 95%; 1H NMR (500 MHz, CDCl3) δ 0.94 (3H, t, J = 7.4 Hz), 1.34 (1H, m), 1.44 (1H, m), 1.65−1.83 (3H, m), 3.82 (3H, s), 4.66 (1H, dd, J = 5.8 and 7.6 Hz), 6.91 (1H, ddd, J = 1.2, 2.4, and 8.3 Hz), 6.91−6.93 (2H, m), 7.26 (1H, t, J = 8.1 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (0.5 mL/min, 7% iPrOH in hexane), giving retention times of 23.8 min (minor S enantiomer) and 26.6 min (major R enantiomer). The retention times were concordant with published values.48 (R)-1-(2-Chlorophenyl)pentan-1-ol (4e)15 (Table 1, entry 18). Yield 156 mg, 79%; 1H NMR (500 MHz, CDCl3) δ 0.91 (3H, t, J = 7.1 Hz), 1.31−1.52 (4H, m), 1.66−1.82 (2H, m), 1.88 (1H, br), 5.13 (1H, dd, J = 4.5 and 8.1 Hz), 7.20 (1H, dt, J = 1.7 and 7.6 Hz), 7.27−7.34 (2H, m), 7.54 (1H, dd, J = 1.6 and 7.7 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralpak OB-H column (1 mL/min, 0.3% i PrOH in hexane), giving retention times of 16.1 min (major R enantiomer) and 19.8 min (minor S enantiomer). The retention times were concordant with published values.39 (R)-1-Thiophen-2-ylpentan-1-ol (5a)49 (Table 1, entry 19). Yield 140 mg, 82%; 1H NMR (500 MHz, CDCl3) δ 0.90 (3H, t, J = 7.2 Hz), 1.26−1.50 (4H, m), 1.78−2.00 (3H, m), 4.92 (1H, t, J = 6.7 Hz), 6.96− 6.98 (2H, m), 7.25 (1H, dd, J = 1.6 and 4.6 Hz). Enantioselectivity was 6130

DOI: 10.1021/acs.joc.8b00929 J. Org. Chem. 2018, 83, 6127−6132

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The Journal of Organic Chemistry

(2) Pu, L.; Yu, H.-B. Catalytic Asymmetric Organozinc Additions to Carbonyl Compounds. Chem. Rev. 2001, 101, 757−824. (3) Pu, L. Asymmetric Alkynylzinc Additions to Aldehydes and Ketones. Tetrahedron 2003, 59, 9873−9886. (4) Hatano, M.; Miyamoto, T.; Ishihara, K. Recent Progress in Selective Additions of Organometal Reagents to Carbonyl Compounds. Curr. Org. Chem. 2007, 11, 127−157. (5) Schmidt, F.; Stemmler, R. T.; Rudolph, J.; Bolm, C. Catalytic Asymmetric Approaches towards Enantiomerically Enriched Diarylmethanols and Diarylmethylamines. Chem. Soc. Rev. 2006, 35, 454− 470. (6) Trost, B. M.; Weiss, A. H. The Enantioselective Addition of Alkyne Nucleophiles to Carbonyl Groups. Adv. Synth. Catal. 2009, 351, 963− 983. (7) Yus, M.; Gonzalez-Gomez, J. C.; Foubelo, F. Catalytic Enantioselective Allylation of Carbonyl Compounds and Imines. Chem. Rev. 2011, 111, 7774−7854. (8) Pellissier, H. Enantioselective Titanium-Catalysed 1,2-Additions of Carbon Nucleophiles to Carbonyl Compounds. Tetrahedron 2015, 71, 2487−2524. (9) Review: Collados, J. F.; Sola, R.; Harutyunyan, S. R.; Macia, B. Catalytic Synthesis of Enantiopure Chiral Alcohols via Addition of Grignard Reagents to Carbonyl Compounds. ACS Catal. 2016, 6, 1952−1970. (10) Weber, B.; Seebach, D. Ti-TADDOLate-Catalyzed, Highly Enantioselective Addition of Alkyl- and Aryl-titanium Derivatives to Aldehydes. Tetrahedron 1994, 50, 7473−7484. (11) Côté, A.; Charette, A. B. General Method for the Expedient Synthesis of Salt-Free Diorganozinc Reagents Using Zinc Methoxide. J. Am. Chem. Soc. 2008, 130, 2771−2773. (12) Hatano, M.; Gouzu, R.; Mizuno, T.; Abe, H.; Yamada, T.; Ishihara, K. Catalytic Enantioselective Alkyl and Aryl Addition to Aldehydes and Ketones with Organozinc Reagents Derived from Alkyl Grignard Reagents or Arylboronic Acids. Catal. Sci. Technol. 2011, 1, 1149−1158. (13) Muramatsu, Y.; Harada, T. Catalytic Asymmetric Alkylation of Aldehydes with Grignard Reagents. Angew. Chem., Int. Ed. 2008, 47, 1088−1090. (14) Muramatsu, Y.; Harada, T. Catalytic Asymmetric Aryl Transfer Reactions to Aldehydes with Grignard Reagents as Aryl Source. Chem. Eur. J. 2008, 14, 10560−10563. (15) Muramatsu, Y.; Kanehira, S.; Tanigawa, M.; Miyawaki, Y.; Harada, T. Catalytic Enantioselective Alkylation and Arylation of Aldehydes by Using Grignard Reagents. Bull. Chem. Soc. Jpn. 2010, 83, 19−32. (16) Itakura, D.; Harada, T. Catalytic Enantioselective Arylation of Aldehydes by Using Functionalized Grignard Reagents Generated from Aryl Bromides. Synlett 2011, 2011, 2875−2879. (17) Da, C.-S.; Wang, J.-R.; Yin, X.-G.; Fan, X.-Y.; Liu, Y.; Yu, S.-L. Highly Catalytic Asymmetric Addition of Deactivated Alkyl Grignard Reagents to Aldehydes. Org. Lett. 2009, 11, 5578−5581. (18) Liu, Y.; Da, C.-S.; Yu, S.-L.; Yin, X.-G.; Wang, J.-R.; Fan, X.-Y.; Li, W.-P.; Wang, R. Catalytic Highly Enantioselective Alkylation of Aldehydes with Deactivated Grignard Reagents and Synthesis of Bioactive Intermediate Secondary Arylpropanols. J. Org. Chem. 2010, 75, 6869−6878. (19) Fernandez-Mateos, E.; Macia, B.; Ramon, D. J.; Yus, M. Catalytic enantioselective addition of MeMgBr and other Grignard reagents to aldehydes. Eur. J. Org. Chem. 2011, 2011, 6851−6855. (20) Fernandez-Mateos, E.; Macia, B.; Yus, M. Catalytic Enantioselective Addition of Alkyl Grignard Reagents to Aliphatic Aldehydes. Adv. Synth. Catal. 2013, 355, 1249−1254. (21) Zheng, L.-S.; Jiang, K.; Deng, Y.; Bai, X.-F.; Gao, G.; Gu, F.-L.; Xu, L.-W. Synthesis of Ar-BINMOL Ligands by [1,2]-Wittig Rearrangement to Probe Their Catalytic Activity in 1,2-Addition Reactions of Aldehydes with Grignard Reagents. Eur. J. Org. Chem. 2013, 2013, 748−755. (22) For reviews of the methods using more than stoichiometric amount of chiral ligands, see: (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley: New York, 1994; Chapter 5. (b) Luderer, M. R.; Bailey, W. F.; Luderer, M. R.; Fair, J. D.; Dancer, R. J.; Sommer, M. B.

determined by HPLC analysis using a Chiralcel OB-H column (2 mL/min, 2% iPrOH in hexane), giving retention times of 12.6 min (minor S enantiomer) and 13.7 min (major R enantiomer). The retention times were concordant with published values.39 (R)-1-Thiophen-2-ylheptan-1-ol (5b)42 (Table 1, entry 21). Yield 157 mg, 79%; 1H NMR (500 MHz, CDCl3) δ 0.88 (3H, t, J = 6.9 Hz), 1.23−1.37 (7H, m), 1.45 (1H, m), 1.79−1.95 (3H, m), 4.92 (1H, t, J = 6.7 Hz), 6.96−6.98 (2H, m), 7.24 (1H, dd, J = 1.7 and 4.6 Hz). Enantioselectivity was determined by HPLC analysis using a Chiralcel OB-H column (1 mL/min, 3% iPrOH in hexane), giving retention times of 8.9 min (minor S enantiomer) and 10.1 min (major R enantiomer). The retention times were concordant with published values.42 (R)-1-Phenylhept-1-en-3-ol (6a)50 (Table 1, entry 23). Yield 156 mg, 82%; 1H NMR (500 MHz, CDCl3) δ 0.92 (3H, t, J = 7.3 Hz), 1.32−1.46 (5H, m), 1.56−1.70 (2H, m), 4.28 (1H, q, J = 6.5 Hz), 6.23 (1H, dd, J = 6.8 and 15.9 Hz), 6.57 (1H, d, J = 15.9 Hz), 7.24 (1H, m), 7.33 (2H, m), 7.49 (2H, m). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 9% iPrOH in hexane), giving retention times of 8.2 min (major R enantiomer) and 13.0 min (minor S enantiomer). The retention times were concordant with published values.50 (R)-2-Methylhept-1-en-3-ol (6b)51 (Table 1, entry 24). Yield 152 mg, 59%; 1H NMR (500 MHz, CDCl3) δ 0.91 (3H, d, J = 7.2 Hz), 1.22− 1.38 (4H, m), 1.50−1.62 (3H, m), 1.72 (3H, t, J = 1.0 Hz), 4.06 (1H, t, J = 6.5 Hz), 4.83 (1H, m), 4.93 (1H, m). Enantioselectivity was determined by HPLC analysis of the benzoate derivative using a Chiralcel OB-H column (1 mL/min, 0.1% iPrOH in hexane), giving retention times of 5.6 min (minor S enantiomer) and 7.9 min (major R enantiomer). The retention times were concordant with published values.15 Benzoate derivative of 6b: 1H NMR (500 MHz, CDCl3) δ 0.91 (3H, d, J = 7.2 Hz), 1.28−1.42 (4H, m), 1.70−1.85 [5H, m, including t (J = 1.0 Hz, 3H) at 1.80], 4.92 (1H, t, J = 1.5 Hz), 5.03 (1H, m), 5.42 (1H, t, J = 6.8 Hz), 7.44 (2H, m), 7.56 (1H, tt, J = 1.3 and 7.5 Hz), 8.07 (2H, m). (R)-1-Phenylheptane-3-ol (7)52 (Table 1, entry 25). Yield 31 mg, 16%; 1H NMR (500 MHz, CDCl3) δ 0.91 (3H, t, J = 7.0 Hz), 1.25−1.55 (7H, m), 1.70−1.85 (2H, m), 2.67 (1H, m), 2.79 (1H, m), 3.63 (1H, tt, J = 4.4 and 7.8 Hz), 7.18−7.24 (2H, m), 7.27−7.32 (3H, m). Enantioselectivity was determined by HPLC analysis using a Chiralcel OD-H column (1 mL/min, 2% iPrOH in hexane), giving retention times of 17.2 min (major R enantiomer) and 27.4 min (minor S enantiomer). The retention times were concordant with published values.52

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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.8b00929. NMR spectra and LC charts of products (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Toshiro Harada: 0000-0002-9818-5386 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by KAKENHI (15K05500) from Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.

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REFERENCES

(1) Soai, K.; Niwa, S. Enantioselective Addition of Organozinc Reagents to Aldehydes. Chem. Rev. 1992, 92, 833−856. 6131

DOI: 10.1021/acs.joc.8b00929 J. Org. Chem. 2018, 83, 6127−6132

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DOI: 10.1021/acs.joc.8b00929 J. Org. Chem. 2018, 83, 6127−6132