Stereoselective Synthesis of 4H-5, 6-Dihydro-1, 3-thiazine and 4, 5-Dihydrothiazole Derivatives by Use of Imidothioic Acid Esters

Abstract

A general synthetic method of allylimidothioates (1) was established by the reactions of allyl bromides with various thioamides in aprotic solvents under mild conditions.
5-Bromo-4H-5, 6-dihydro-1, 3-thiazines (2) and 4-bromomethyl -4, 5-dihydrothiazoles (3) were synthesized by intramoleculer cyclization of the allylimidothioates (1) with N-bromosuccinimide (NBS) or bromine in dichloromethane at room temperature. In these reactions, (E)-1 gave trans-2 and anti-3; on the other hand, (Z) -1 afforded cis-2 and syn-3, respectively.
Reaction of 3-butenylimidothioates (1h) with NB S afforded only 2-substituted-3-bromothiolane derivative (20) instead of expected tetrahydrothiazepine (21) or dihydrothiazine derivative (22).
Synthetic applications and plausible mechanisms of these reactions were described.