MACROCYCLES BY RING-CLOSING METATHESIS

The ruthenium carbene complexes 1 and 2 (0.05-5 mol %) catalyse highly efficient macrocyclization reactions of 1,omega-dienes by ring-closin g metathesis (RCM). Key parameters for successful RCM are (i) the pres ence of a functional group which serves as a relay entity that assembl es the reacting sites, (ii) an appropriate distance between this polar group and the alkenes to be metathesized, and (iii) low steric conges tion near the double bonds. Contrary to previous assumptions, however, the ring size formed and the conformational predisposition of the sub strates for ring closure turned out to be of minor importance. These a spects are illustrated by some straightforward syntheses of macrocycli c lactones, lactams, ethers and ketones, including the musk odored per fume ingredients Exaltolide, Exaltone and Arova 16, of the macrolide r ecifeiolide (24), as well as of the alkaloids epilachnene (40) and its homologue 9-propyl-10-azacyclododecan-12-olide (39), which are active principles of the defense secretions of the pupae of the mexican beet le Epilachnar varivestis.