Regioselective synthesis of substituted pterocarpans and pterocarpenes. Lewis acid Ti(IV) promoted formal (3 + 2) cycloaddition reactions

Article abstract of DOI:10.1016/0040-4020(95)01052-1

A synthesis of novel pterocarpans (8a-3, 10a-c and 11a-e) and pterocarpenes (7a-d and 9a-c) has been carried out. This method involves the Lewis acid Ti(IV) promoted formal (3 + 2) cycloaddition reaction of 2-alkoxy-1,4-benzoquinones (6a-c) with appropriately substituted 2H-chromenes (1a-b, 2a-b and 5) at -78°C.