Chemical Transformation of Protoberberines. XI. A Novel Synthesis of 2, 3, 10, 11-Tetraoxygenated Protoberberine Alkaloids from Corresponding 2, 3, 9, 10-Tetraoxygenated Protoberberine Alkaloids

Abstract

2, 3, 9, 10-Tetraoxygenated protoberberin alkaloids, berberine (1a), palmatine (1b), and coptisine (1c), were efficiently converted into the corresponding 12-hydroxy-2, 3, 10, 11-tetraoxygenated protoberberines (6a, 6b, 6c) through an oxidative C₈-C_8a bond cleavage with m-chloroperbenzoic acid, followed by the enamide photo-cyclization. On successive treatment with diethyl chlorophosphate and sodium in liquid ammonia, the 12-hydroxy derivatives (6a, 6b, 6c) underwent reductive dehydroxylation to produce the corresponding 2, 3, 10, 11-tetraoxygenated protoberberines, tetrahydropseudoberberine (4a), (±) -xylopinine (4b), and tetrahydropseudocoptisine (4c), respectively.