Synthesis of 1,2-thiazines and 1,2-thiazepines by ring expansion

Article abstract of DOI:10.1002/ardp.19923250803

The β-ketosultames 3 and 11 are transformed by aldol condensation into the corresponding alkylidene derivatives 4, 5 and 12. Epoxidation of 5 and 12 leads to the epoxyketones 6 and 13 which isomerize by boron trifluoride etherate to 1,2-thiazine 7 and 1,2