Synthesis of indenol- and azulenol derivatives via platinum dichloride-catalyzed intramolecular hydroxy- or alkoxycyclization of cyclic dienynes

(Chemical Equation Presented) Platinum dichloride-catalyzed hydroxy- or alkoxycyclization of cyclohexadienynes gives indenol derivatives, whereas hydroxy- or alkoxycyclization of cycloheptadienynes produces azulenol derivatives. The cyclization reaction proceeds via a cyclopropyl platinacarbene intermediate and allows for the direct stereocontrol of three contiguous stereogenic centers of the fused bicyclic skeletons. The transient reactive intermediate obtained from PtCl₂-catalyzed cyclization reaction of a cyclohexadienyndiol can be trapped intramolecularly by a hydroxyl group to afford an oxatricyclo[5.4.0.0^4,8]-undecane ring skeleton with extreme diastereoselectivity.