Chiral Synthesis via Organoboranes. 40. Selective Reductions. 55. A Simple One-Pot Synthesis of the Enantiomers of (Trifluoromethyl)oxirane. A General Synthesis in High Optical Purities of α-Trifluoromethyl Secondary Alcohols via the Ring-Cleavage Reactions of the Epoxide

Abstract

An extremely efficient one-pot asymmetric synthesis of either enantiomer of (trifluoromethyl)oxirane (3,3,3-trifluoro-1,2-epoxypropane, 4) in 64% yield and 96% ee has been achieved via the asymmetric reduction of the commercially available l-bromo-3,3,3-trifluoro-2-propanone with either (+)- or (−)- 5-chlorodiisopinocampheylborane (Aldrich: DIP-Chloride), followed by ring closure of the intermediate chloroborinate, IpcBCl[OCH(CH2Br)CF3]. The ring cleavage reactions of 4 provide a general synthesis of chiral trifluoromethyl carbinols without loss of optical activity. Thus we have synthesized 1-amino-3,3,3-trifluoro-2-propanol, 1-azido-3,3,3-trifluoro-2-propanol, 1-(diethylamino)- 3,3,3-trifluoro-2-propanol, 1-cyano-3,3,3-trifluoro-2-propanol, 1,1,1-trifluoro-2-propanol, 1,1,1-tri- fluoro-2-octanol, 1-phenyl-3,3,3-trifluoro-2-propanol, 1-ethoxy-3,3,3-trifluoro-2-propanol, and 1,2- dihydroxy-3,3,3-trifluoropropane, in 61–88% yields and in 96% ee by the cleavage of 4 with the appropriate nucleophile. © 1995, American Chemical Society. All rights reserved.