Transition-metal-free skeletal editing of benzoisothiazol-3-ones to 2,3-dihydrobenzothiazin-4-ones via single-carbon insertion†

Abstract

Transition-metal-free ring expansion of benzoisothiazol-3-ones has been established to synthesize 2,3-dihydrobenzothiazin-4-ones via single-carbon insertion. A variety of 2,3-dihydrobenzothiazin-4-ones have been prepared with good yields. The use of aldehydes and ketones resulted in the formation of 2-substituted and 2,2-disubstituted 2,3-dihydrobenzothiazin-4-ones using HI and NH₄I as additives. Furthermore, the easily prepared 1-(chloromethyl)-1,4-diazabicyclo[2.2.2]octan-1-ium chloride [DABCO·DCM] was first utilized as the methylene source for the selective synthesis of 2,3-dihydrobenzothiazin-4-ones and bis-2,3-dihydrobenzothiazin-4-ones.