Intramolecular titanium-promoted deoxygenative cyclization to 9-substituted-1,2,3,4-tetrahydrofluorene skeleton

The Mukaiyama aldol reaction of 2-aryl-1-cyclohexene-1-carboxaldehydes with phenyl trimethylsilyl ketene acetal unexpectedly resulted in the formation of 9-substituted-1,2,3,4-tetrahydrofluorene derivatives via a novel intramolecular titanium-promoted deoxygenative cyclization. By successive treatment of the corresponding allyl alcohols with n-butyllithium and titanium tetrachloride, the cyclization products were obtained in good yields.