The reaction of α-haloketones with N-alkyl benzothiazolium salts

Phenacyl chloride ( 1a ) reacts with the 3-methylbenzothiazolium quaternary salt ( 2 ) to give 4-methyl-2-benzoyl-4H-1,4-benzothiazine ( 4a ). A mechanism is discussed. Secondary α-haloketones give benzothiazolines. Merocyanine dyes are formed by the reaction of 2 with carbanions. It is shown that 2 functions as a hydride ion abstractor in the formation of merocyanine dyes.