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 alpha,beta-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. (c) 2007 Elsevier Ltd. All rights reserved.