Blocking group-directed diastereoselective total synthesis of (±)-α-noscapine

A new approach for the diastereoselective synthesis of (±)-α-noscapine, a phthalide tetrahydroisoquinoline alkaloid exhibiting several biological activities, is described. The strategy features a blocking group-directed Bischler–Napieralski reaction followed by diastereoselective reduction (α/β>23:1). One of the key intermediates, phthalide-3-carboxylic acid, could be efficiently prepared from simple benzoic acid derivative and glyoxylic acid in one-pot.