Synthesis of Dihydro-1,4-oxathiins by Action of Chlorine on 1,3-Oxathiolanes

Article abstract of DOI:10.1021/jo00233a012

A new convenient synthesis of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxylic acid derivatives 1 has been achieved by using the action of chlorine on 2-methyl-N-phenyl-1,3-oxathiolane-2-acetamide (4a) and 2-methyl-1,3-oxathiolane-2-acetic acid methyl ester (4b).From the initially formed chlorosulfonium salts 16 unobserved transient sulfenyl chlorides 5 were generated, followed by cyclization to probable oxonium ion 18 to produce dihydrooxathiins 1.In the chlorinolysis reactions of 4a and 4b minor byproducts were formed: respectively 2,3-dichloro-2-methyl-1,4-oxathiin-3-carboxanilide 12a and its methyl ester analogue 12b.While 12b was stable, 12a was unstable, transforming to the corresponding 2-chloromethyl compound 13.The mechanism of formation of 13 as well as relative stability of dichlorides 12a, 12b, and related compounds is also discussed.