SELECTIVE SYNTHESIS OF FERROCENES

We have developed a new one pot procedure for the selective functional ization of the 1' position in ferrocenecarbaldehyde, with fair yields (up to 70%) and good regioselectivity (>90/10). Our method uses lithiu m N-methylpiperazide as a temporary protecting group of the aldehyde f unction and directing group for lithiation on the unsubstituted cyclop entadienyl ring of ferrocene. The extension of this new method with en antiomerically pure 2-substituted ferrocenecarbaldehydes provides an e asy access to various enantiomerically pure 1,2,1'-trisubstituted ferr ocenes with three different groups. Finally, when applying our method for the lithiation of 1,1'-ferrocenedicarbaldehyde with a chiral amine , we found a one pot synthesis of 1,2,1',2'-tetrasubstituted C-2-symme trical ferrocenes with very high enantiomeric excesses (>99%). Further more, changing the experimental conditions allows us to obtain 1,2,1'- trisubstituted ferrocenes with a very good enantioselectivity (up to 9 6%). The first chiral enantiomerically pure 2-substituted 1,1'-(beta-o xa-trimethylene)ferrocenes and the first chiral enantiomerically pure C-2-symmetrical-disubstituted 1,1'-(beta-oxa-trimethylene)ferrocene we re also synthesized. (C) 1998 Elsevier Science S.A. All rights reserve d.