Enantioselective syntheses of various chiral multicyclic compounds with quaternary carbon stereocenters by catalytic intramolecular cycloaddition

The intramolecular cycloaddition of 1,n-diene-ynes (n = 4-6), where alkyne and alkene moieties are connected by a 1,1-disubstituted alkene, was examined using a chiral rhodium catalyst, and various types of cycloadducts with quaternary carbon stereocenter(s) were obtained in high to excellent enantiomeric excess. In the case of 1,4-diene-ynes, tricyclic, bicyclic, and spirocyclic compounds were obtained depending upon the substituents at the 2-position of the 1,4-diene moiety and those at their alkyne termini. On the other hand, 1,5- and 1,6-diene-ynes gave tricyclic and bicyclic compounds, which included medium-sized ring systems. The mechanistic considerations for different reaction pathways and the synthetic transformation of tricyclic products into functionalized spirocyclic compounds are also described. The reaction of enediynes, where two alkyne moieties are connected by a 1,1-disubstituted alkene, was also examined, and sterically strained tricyclic compounds with two carbon stereocenters were obtained.