Applications of the Chiral Auxiliaries DIOZ and TRIOZ for Conjugate Additions and Comparison with Other Auxiliaries

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, i Pr, 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 ‐enolate‐nitronate 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 ).