Photoisomerization of 2H,6H-Thiin-3-one 1-Oxides to 3H,7H-Oxathiepin-4-ones

Article abstract of DOI:10.1002/hlca.19930760311

Oxidation of 2H,6H-thiin-3-ones 1a-c with 3-chloroperbenzoic acid affords the corresponding 1-oxides 2a-c.On irradiation (350 nm) in either benzene or MeCN, these cyclic sulfoxides 2 isomerize to 3H,7H-1,2-oxathiepin-4-ones 3.The tetramethyl derivative 3a is isolated by flash chromatography at -10 deg C, but at higher temperatures, it undergoes ring contraction and H2O elimination to give 4,4-dimethyl-2-(2-methylprop-2-enylidene)thietan-3-one (4).Dimethyloxathiepinones 3b and 3c undergo ring contraction in MeOH to afford 1-(4-methylthiophen-2-yl)ethanone (5) and two diastereoisomeric 4,4-dimethyl-2-methoxy-2-(1-methoxyethyl)thietan-3-ones (6 and 7, respectively).