Construction of Hexahydrophenanthrenes By Rhodium(I)-Catalyzed Cycloisomerization of Benzylallene Substituted Internal Alkynes through C-H Activation

The treatment of benzylallene-substituted internal alkynes with [RhCl(CO)(2)](2) effects a novel cycloisomerization by C(sp(2))-H bond activation to produce hexahydrophenanthrene derivatives. The reaction likely proceeds through consecutive formation of a rhodabicyclo[4.3.0] intermediate, s-bond metathesis between the C(sp2)-H bond on the benzene ring and the C(sp(2))-Rh-III bond, and isomerization between three sigma-, pi-, and sigma-allylrhodium(III) species, which was proposed based on experiments with deuterated substrates.