A rapid approach to ferrocenophanes via ring-closing metathesis

The synthesis of [4]ferrocenophanes containing a (Z)-1,4-but-2-endiyl bridg e is described. Starting from either achiral (R = H), meso (R = Me, Ph) or scalemic (R = Me, 4-MeOC6H4) 1,1 ' -di{CHR(OAc)}ferrocenes, vinylation with a mixture of vinyl magnesium chloride and zinc chloride proceeds readily a nd with significant retention of configuration to give allylferrocenes in a n isomer ratio of > 3:1. Ring-closing metathesis with Ru(CHPh)Cl-2(PCy3)(2) results in conversion of the achiral (R = H) and an the meso-diastereoisom ers (R = Me, Ph, 4-MeOC6H4) to their corresponding cis-disubstituted [4]fer rocenophanes. Only a single trans-disubstituted [4]ferrocenophane was synth esised (R = Me), the larger substituents preventing cyclisiation by this me thod. (C) 2001 Elsevier Science BN. All rights reserved.