Gas-phase cyclisation reactions of 1-(2-arylthiophenyl)alkaniminyl and 2-(aryliminomethyl)thiophenoxyl radicals

Flash vacuum pyrolysis (FVP) of the oxime ethers 12-14 and of the sulfides 18-20 at 650 degreesC (10(-2)-10(-3) Torr) gave products derived from the corresponding iminyl and thiophenoxyl radicals. In all cases, benz[d]isothiazoles (e.g., 26) are formed as major products via S(H)i mechanisms though the yields are greatest with the iminyl precursors. Alternative pathways observed from the thiophenoxyls in specific cases include the formation of the anilinobenzothiophene 36 and of dibenzothiophene 23, via an S(H)i process and a spirodienyl rearrangement, respectively. There is no evidence for significant interconversion of the iminyl and thiophenoxyl species.