Asymmetric synthesis of (+)-polyanthellin A.

A concise and convergent route to (+)-polyanthellin A is presented. This synthesis features a diastereoselective cyclopropane/aldehyde [3+2] cycloaddition to install the hydroisobenzofuran core. The use of MADNTf(2) as a potent, bulky Lewis acid was essential to allow a labile beta-silyloxy aldehyde to be used in the cycloaddition. Other key steps include a ring-closing metathesis and a selective olefin oxidation.