Ru(II)-catalyzed ring closing metathesis in stereoselective spiroannulations and cascade reactions of cyclic dipeptide substrates

Several Ru(II)-catalyzed ring closing metathesis (RCM) reactions have been reviewed where the substrates were diene or enyne geminally disubstituted c yclic dipeptide derivatives. The RCM reactions are highly useful for the pr eparation of spiroannulated cyclic dipeptides as precursors for conformatio nally restricted cyclic alpha-amino acid derivatives. Five-, six- and seven -membered rings can be formed. Six- and seven-membered rings were formed mo st readily from dienes, five- and six-membered rings from enynes. Cascade r eactions of diene substrates, which were connected by an alkynyl bridge bet ween the two cyclic dipeptide units, yielded bis(cyclic alpha-amino acid) a s precursors for cystine analogues. (C) 2000 Published by Elsevier Science Ltd.