Study on the reaction mechanism of Heck-oxyarylation of 2H-chromenes

The Heck-oxyarylation reaction of deuterium labeled 2H-chromenes (12,15) has been studied whose synthesis was achieved in four steps starting from the readily available 7-benzyloxychromane (9). Since the deuterium label was not affected in the course of the oxyarylation, the formation of the neutral achiral intermediate 7 could be ruled out as a possible reaction pathway and a reason for the lack of enantioselectivity in asymmetric Heck-oxyarylations. This also allowed the simple synthesis of 6a- and 11a-deutero-3-benzyloxypterocarpanes (13a, b).