Asymmetric synthesis of (+)-polyanthellin A

A concise and convergent route to (+)-polyanthellin A which features a diastereoselective cyclopropane/aldehyde [3+2] cycloaddition to install the hydroisobenzofuran core is described. The key steps in the synthesis include a ring-closing metathesis and a selective olefin oxidation in presence of MADNT[f.sub.2] as a potent, bulky Lewis acid required to facilitate a labile [beta]-silyloxy aldehyde to be used in the cycloaddition.