Effects of solvent and lithiating agent on stereoselectivity in lithiation of chiral 1,1'-bis(oxazolinyl)ferrocenes

Abstract

The analysis of phosphorylation products was carried out to investigate the stereoselectivity change in lithiation of 1,1'-bis[(S)-2-(4-R-oxazolinyl)]ferrocene (1) with varying reaction conditions such as solvents, lithiating agents, and temperatures. Monolithiation with butyllithiums in Et(2)O led to the configuration corresponding to (R)-2, while use of THF favors (S)-2. Dilithiation with sec-BuLi or t-BuLi in Et(2)O led to the configuration corresponding to (R,S)-3. However, the step-by step lithiation at different temperatures with sec-BuLi in Et(2)O provided the dilithiated species corresponding to (R,R)-3. sec-BuLi in THF was special to give (S,S)-3 as the major product. Copyright (C) 1996 Elsevier Science Ltd