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An investigation into the origins of the enantioselectivity observed in oxazaborolidine-catalyzed reductions of ketones was carried out by examination of the reaction surfaces generated using the MNDO Hamiltonian.The reports describing the enantioselective reduction of ketones using stoichiometric borane in the presence of catalytic amounts of chiral oxazaborolidines represent a significant advance in rational reagent design (Figure l).l These reactions presumably occur by the following sequence: (a) complexation of borane to the ring nitrogen; (b) coordination of the ketone oxygen to the ring boron; (c) hydrogen transfer from the NBH3-unit to the carbonyl carbon via a six-membered cyclic transition state. The (1) (a) Corey, E. J.; Bakshi, R. K.; Shibata, S . J. Am. Chem. SOC. 1987, 109,5551. (b) Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen, C.-P.; Singh, V. K. Sakurai, Y.; Ito, K.; Hirao, A.; Natmhrma, S. Bull. Chem. SOC. Jpn. 1987, 60, 395. (m) Rao, A. V. R.; Gurjar, M. K.; Shanna, P. A.; Kaiwar, V.

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Abstract

d, Jcp = 30.7 Hz, CO). 3-Chloro-3-fluoro-2,4-pentanedione (5c) was prepared starting from 4c; reaction time 2 h; eluting system for flash chromatography n-hexane/CHzClz, 8515; yield 95%, 'H NMR 6 2.48 (d, J = 2.7 Hz); ' BF NMR 6 -126.2 (septet, CF), 197.48 (d, Jcs = 27.0 Hz, CO); IR (film) 2925,1738 (CO) cm-'; MS (CI) m / e 153 and 155 (M+ + 1). 1,3-Dimethyl-5,5-difluorobarbituric acid (5e) was prepared starting from 1,3-dimethylbarbituric acid (4e) and 2.2 equiv of 1; acetonitrile was used as reaction solvent; reaction time 6 h; eluting system for flash chromatography n-hexanelethyl acetate 7:3; yield 95%; mp 9); 'gF NMR 6 -122.8 (d, J 20.36 (CH,), 25.00 (CH,), 64.40 (CHzO), 102.14 (d, J c 2.5 Hz); 'Bc NMR 6 13.83 (CH,), 251.8 J 2.7 Hz); '9C NMR 6 24.95 (CH,), 102.84 (d, Jcp 269.6 Hz, 125-127 "C; 'H NMR 6 3.40 (a); 'H NMR (CDSCN) 6 3.26 (t, J = 0.5 Hz); ' BF NMR 6 -108.7; '9C NMR (CDSCN) 6 29.64 (CH,), 99.61 (t, J c s = 245.5 Hz, CFZ), 150.35 (NCON), 160.97 (t, J c r = 27.8 Hz, COCFJ; IR (Nujol) 1687 (CO), 1448,1304 cm-' ; MS (EI) m / e 192 (M+), 176,135, 107,78.Ethyl 3-fluoro-3-methyl-2-oxobutanoate (7a) was prepared starting from 6a; reaction time 27 h; eluting system for flash chromatography n-hexanelethyl ether, 64; yield 95%; 'H NMR 6 1.39 (3 H, t), 1.64 (6 H, d, J = 21.6 Hz), 4.41 (2 H, 9); '9 NMR 6 -151.4 (septet, J = 21.3 Hz) ('9 NMR 6 -152.0 (septet, J = 21.3 Hz, ref 13)); '9c NMR 6 13.87 (CHJ, 24.14 (d, Jcp = 24.1 Hz, CHJ, 64.00 (CHZO), 97.85 (d, Jcp = 177.9 Hz, CF), 164.08 (COO), 196.82 (d, Jcr = 35.3 Hz, CO), MS (CI) m / e 163 (M+ + l), 143. 3-Fluoro-3-methyl-2-oxopentanoic acid (7b) was prepared starting from 6 b CHCl, saturated with H80, was used 88 reaction solvent; reaction time 24 h; eluting system for flash chromatography CHzClz/ethyl acetate/acetic acid, 5&50:0.5; yield 95%; ' H NMR 6 0.98 (3 H, t), 1.65 (3 H, d, J = 21.8 Hz), 1.9-2.2 (2 H, m); ' BF NMR 6 -160.1 (sextet, J = 21.5 Hz); '9C NMR 6 7.05 (CHJ, CO); I$ ( f i l m ) 3300-2500 (COOH), 1748,1193 cm-'; MS (E11 m / e 148 (M+), 128,121,75. 3-Fluoro-2-oxobutanoic acid (7c) was prepared starting from 6c; reaction time 18 h; eluting system for flash chromatography CHzClz/ethyl acetate/acetic acid, 5Of&O.:o.5; yield 95%; lH NMR (DzO) 6 1.36 (3 H, dd, J = 6.3,25.5 Hz, CHJ, 21.86 (d, J c r = 23.2 Hz, CHJ, 30.39 (d, Jcp = 22.5 Hz, CHJ, 99-95 (d, J c = 182.0 Hz, CF), 163.5 (COOH), 195.5 (d, Jcp = 32.9 Hz, 4.86 (1 H, dq, J = 6.3,46.7 Hz, CHF); ' BF NMR (DzO) b -186.2 (dq, J = 25.6, 47.6 Hz); "C NMR (DzO) 6 12.74 (d, Jcp = 21.6 Hz, CHd, 90.97 (d, J c = 172.7 Hz, CF), 92.90 (d, Jcp = 23.4 Hz, OCO of the hydratetketone), 171.92 (COOH).A efficient process for the commercial preparation of the therapeutically important cholesterol lowering drug synvinolin (2: simvastatin, ZOCOR) from mevinolin (1: lovastatin, MEVACOR) is reported. The synthesis reliea upon deactivation of the &lactone carbonyl toward enolization via conversion to the bis[(tert-butyldimenyl)o~] butylamide 7. An extremely high conversion (99.7%) ester enolate alkylation of 7 affords 8 an...

dures and spectral data ( and 13C NMR, IR, HRMS, and combustion analyses) for compounds 1 and 2, an improved preparation for 1,4-dichlorophthalazine, the preparation of ADmix, and analytical data (HPLC, GLC retention times of the diols or their MTPA esters and the optical rotations of the diols) (6 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information.