Organic heterocyclothiazenes. Part 15. Pyrazolotrithiadiazepines and their rearrangement to 1,2,3-dithiazoles

Abstract

Treatment of 6-bromotrithiadiazepine 1 with Hünig's base in the presence of diphenyldiazomethane 2a gives the hetaryne cycloadduct 3a. Neat thermolysis of this at 210 °C results in very rapid loss of N₂ and ‘HNS’ in a deep-seated rearrangement to give the new indeno-1,2,3-dithiazole ring system 4a. A mechanism proposed for this rearrangement (Schemes 2 and 5) is supported by the isolation of a key intermediate 12 when the cycloadduct 3a is thermolysed in dilute solution at lower temperatures. The intermediate 12 dimerises reversibly to give 13, possibly by a 8-electron ene-type reaction. Other diaryldiazomethanes 2 give analogous hetaryne cycloadducts 3(70–80%) which rearrange similarly when heated to give more complex 1,2,3-dithiazoles 4(20–40%)(Scheme 1).