Dérives de l'imidazo[2,1-b]thiazole. V. Transposition allylique observée au cours de la synthése d'(imino-2 alkyl-3 thiazolinyl-4) acetates d'ethyle et de (dihydro-5,6 imidazo[2,1-b]thiazolyl-3) acetates d'éthyle

Ethyl (6-phenyl-5,6-dihydroimidazo[2,1-b]thiazol-3-yl) acetate hydrobromide shows an allylic transposition in alkaline medium and gives ethyl (6-phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazol-3-ylidene)acetate. This compound possesses an exocyclic double bond which is stable upon acidification. The intermediate ethyl (2-imino-3-alkylthiazolin-4-yl)-acetates undergo an analogous transposition upon treatment with base, which is reversible upon acidification. These transpositions were observed in the pmr data. The steric constraint and π p π conjugation are discussed in this work.