Photochemical rearrangements of 2-azido-4-thiochromanone 1-oxide and 1,1-dioxide: formation of 2H-benzo[f]-1,2-thiazepine derivatives

Abstract

Photolysis of 2-azido-4-thiochromanone 1,1-dioxide in benzene or dichloromethane leads to the formation of 2H-benzo[f]-1,2-thiazepin-5-one 1,1-dioxide, in very good yield. In contrast, the photolysis of the analogous sulfoxide was much more complex and no ring-expansion product could be isolated, although a small amount of a compound believed to be 2-aminothiochromone 1-oxide was formed. Several attempts to prepare the α-azidosulfide analogue, to compare its photochemical behavior, were unsuccessful and a rationale is proposed for the apparent instability of this member of the series.