Asymmetric synthesis of .gamma.,.gamma.-dialkyl-.gamma.-aminobutyric acid analogs and 2,2-disubstituted pyrrolidines. Control of stereochemistry in aminal ring opening by varying the extent of allylic 1,3 strain
A simple asymmetric synthesis of 2-substituted pyrrolidines and 5-substituted pyrrolidinones
摘要:
An efficient procedure for the preparation of the title compounds in high enantiomeric purity has been realized starting from 3-acylpropionic acids. Stereoselective reduction of chiral bicyclic lactams 2a-h, prepared from the corresponding gamma-keto acid and (R)-phenylglycinol, using alane or triethylsilane with titanium tetrachloride provided the N-substituted pyrrolidines and pyrrolidinones, respectively. Subsequent cleavage of the phenylglycinol returned the desired amines and lactams. The enantiomeric purity of these compounds was determined to be > 98% by chiral stationary-phase HPLC.