PPh3-catalyzed ylide cyclization for the controllable synthesis of benzobicyclo[4.3.0] compounds: base effects and scope

A catalytic intramolecular ylide annulation for the controllable construction of benzobicyclo[4.3.0] ring systems with three continuous stereogenic centers is developed in a single manipulation. In the presence of 20 mol % of triphenylphosphine, the reactions of compounds 1a–1f afford benzobicyclo[4.3.0] compounds 3 and 4 as major products, respectively, with excellent diastereoselectivities in good to excellent yields, depending on the base used. In addition, 2-methyl α,β-unsaturated esters 2a–2c also work well to give the corresponding benzobicyclo[4.3.0] compounds with one quaternary carbon center with high diastereoselectivities in good yields under the same conditions.