Theoretical Studies of Ring-Opening Reactions of Phenylcyclobutabenzenol and Its Reactions with Alkynes Catalyzed by Rhodium Complexes

DFT calculations have been carried out to study the Rh-catalyzed site selective ring-opening reactions of phenylcyclobutabenzenol (1a). Our calculations supported that the mechanism involves β-carbon elimination in a rhodium(I) phenylcyclobutabenzenolato complex followed by alcoholysis. The favorable β-carbon elimination involves the cleavage of the C(sp(2))-C(sp(3))(OH)(Ph) bond in 1a, which determines the site selectivity. The mechanism and regioselectivity of the related Rh-catalyzed insertion reaction of the asymmetric alkyne MeC≡CPh with phenylcyclobutabenzenol (1a) was also investigated. The key step involves the alkyne insertion into the Rh-C σ bond of a species resulting from the favorable β-carbon elimination in the rhodium(I) phenylcyclobutabenzenolato complex. The favorable insertion couples the metal-bonded carbon with the methyl-substituted carbon of MeC≡CPh.