A novel tandem cyclization of 2,7- or 2,8-bis-unsaturated esters mediated by (eta(super 2)-propene)TiX2 (X = Cl or O-i-Pr). A facile construction of bicyclo[3.3.0]octane,-[4.3.0]nonane, and -[3.1.0]hexane skeletons

A novel type of cyclizations of acyclic precursors for the preparation of bicyclic systems, consisting of two different kinds of cyclizations in tandem, starting from the title unsaturated compounds, is presented. The initial step is based on the titanium-mediated cyclization of dienes and enynes, followed by the second ring closure through the addition of the resulting carbon-titanium bond to an electron-deficient moiety in the same molecule with accompanying incorporation of an electrophile. Substrates determine the patterns of reactions, with type I occurring with alpha,beta-olefinic esters and type II involving the reactions of alpha,beta-acetylenic esters.