2-Thioxo-1,3-thiazepan-4-ones, a novel class of cyclic dithiourethanes with a 7-membered ring system

Reaction of isothiocyanates 1 with gamma-thiobutyrolactone (2) in alkaline medium yielded 4-thiocarbamoylthiobutyric acids 3 after acidification, whic h could be cyclized to the 2-thioxo-1,3-thiazepan-4-ones 6. Additional reac tions were observed with the formation of 6t from p-phenylenediisothiocyana te (1s) and with the formation of 6w from benzyl isothiocyanate (1t). 3-Ace tylamino-gamma-thiobutyrolactone (7) could also be used in this reaction yi elding the butyric acid derivatives 3u-3w, Cyclization yielded the 1,3-thia zepane derivatives 6x, y which rearranged under ring contraction to the 1,3 -thiazinanes 8a, b.