Reaction of furans with trithiazyl trichloride: a new synthesis of isothiazoles

Abstract

Trithiazyl trichloride 1 converts 2,5-diphenylfuran into 5-benzoyl-3-phenylisothiazole 2 regiospecifically and in high yield. This is a new ring opening of furans and a new synthesis of isothiazoles. 2,5-Bis(4-methylphenyl)furan, 3-bromo-2,5-diphenylfuran, 2,3,5-triphenylfuran, 2,5-di-tert-butylfuran and its 3-chloro and 3-bromo derivatives react in an entirely analogous manner to give the corresponding isothiazoles (55–85%) in synthetically useful, one-pot, conversions. 2,5-Diphenylthiophene reacts more slowly with the trimer 1 to give the same product, 2, as the corresponding furan, probably by oxidation of the analogous thiobenzoyl compound by the reagent, which is shown to oxidise thiobenzophenone to benzophenone very rapidly. Tetraphenylcyclopentadienone 8 reacts rapidly with the trimer to give 3,4,5,6-tetraphenyl-2(1H)-pyridone 10 (56%). Possible mechanisms in which the monomer, Cl–SN, is the reacting species are proposed for all of these reactions.