Chiral sulfur-containing 1,2-disubstituted ferrocenes

Enantiopure 1-t-butylsulfinyl-2-subsituted ferrocenes were synthesized in reactions of (SR, 1S,2R)-1-t-butylsulfinyl-2-lithioferrocene (11) with various electrophiles in good yields. (SR,1S,2R)-1-t-Butylsulfinyl-2-formylferrocene (19), prepared this way, underwent complete stereoselective addition reactions with Grignard reagents under chelation controlled conditions with titanium tetraisopropoxide. 1,4-Addition reactions of selected a,P-unsaturated esters with cuprate reagents gave mixtures of two diastereomers. The lack of stereoselectivity in these 1,4-addition reactions is due presumably to the remote reactive site (C-3') and the flexibility of the side chain of the ester. A stereoselective cationic displacement reaction of (1S,2R,L'S)-1-(t-butylsulfonyl)-2-[alpha-(2-propenoyl)oxybenzyl]ferrocene (44) with 1-acetoxy-1,3-butadiene was found to produce (1S,2R,1'S)-1-(t-butylsulfonyl)-2-(5'-oxo-1'-phenyl-3'-pentenyl)ferrocene (45). (C) 1998 Elsevier Science Ltd. All rights reserved.