Applications of the chiral auxiliaries DIOZ and TRIOZ for conjugate additions and comparison with other auxiliaries

Abstract

A number of N-acryloyl-, N-crotonoyl-, N-(3,3,3-trifluorocrotonoyl)-, N-cinnamoyl-, and N-(3-nitroacryloyl)-4-isopropyl- or -4-phenyl-oxazolidin-2- ones with geminal diphenyl substitution, i.e., 7-15, have been prepared and used for conjugate additions of organocuprate reagents (Me, iPr, Ph, 4-MeOPh) in the β-carbonyl (Table 2) and in the α-carbonyl position (NO 2-derivative 11 in Scheme 3). The yields and diastereoselectivities are compared with previously tested enoyl-oxazolidinones (Table 2). Highest diastereoselectivities (>90%) are always observed with the 4-Ph derivatives (Hruby effect). Nitroacryloyl-oxazolidinones and a corresponding phenylmenthol ester undergo less diastereoselective additions (Scheme 3). A 3-(1-methylethyl)-5,5-diphenyloxazolidin-2-one (DIOZ)-derived Li 2-enolatenitronate was also tested for α-carbonyl alkylation (Scheme 4). The X-ray crystal structures of three acryloyl-oxazolidinones and of four adducts are described (Tables 1 and 3), and they serve for configurational assignments and description of the stereochemical courses of the additions and alkylation. Possible applications of the nitro compounds for the preparation of β 2-amino acids are discussed (Scheme 2). © 2010 Verlag Helvetica Chimica Acta AG.