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.