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 cyclic dipeptide derivatives. The RCM reactions are highly useful for the preparation of spiroannulated cyclic dipeptides as precursors for conformationally restricted cyclic α-amino acid derivatives. Five-, six- and seven-membered rings can be formed. Six- and seven-membered rings were formed most readily from dienes, five- and six-membered rings from enynes. Cascade reactions of diene substrates, which were connected by an alkynyl bridge between the two cyclic dipeptide units, yielded bis(cyclic α-amino acid) as precursors for cystine analogues.