Abstract
Reaction of 3-methyl-2-phenylbenzothiazolium iodide (I) and metal hydride (LiAlH4 and NaBH4), when carried out in air, gave o-(N-benzoyl-N-methylamino)phenyl disulfide (III) as the main product but, when the reaction was carried out in a nitrogen stream, 3-methyl-2-phenylbenzothiazoline (II) was obtained as the main product. Reaction of I and phenylmagnesium bromide gave 3-methyl-2, 2-diphenylbenzothiazoline (VII) alone, either in air or in a nitrogen stream. Reaction of 3-methylbenzothiazolium iodide (VI) and phenylmagnesium bromide in air gave III as the main product, while II was the main product when the reaction was carried out in a nitrogen stream. From the stability of benzothiazolines in air, from the reaction of II with lithium aluminum hydride, phenylmagnesium bromide, and potassium hydroxide, and from the fact that the oxidative ring cleavage reaction of 5-chloro-3-methyl-2-phenylbenzothiazoline (XI) is accelerated by the addition of a radical reaction promotor, a radical mechanism in which benzothiazolines formed during the synthetic process undergo auto-oxidation by oxygen was proposed as the mechanism for the formation of an oxidative ring cleavage product.
