Structure and thermal reactivity of some 2-substituted 1,3-oxathiolane S-oxides

Isomerisation of 2-benzylidene-1,3-dioxolane to 3-phenylbutyrolactone occurs readily under flash vacuum pyrolysis (FVP) conditions. 2-Diphenylmethyl-1,3-oxathiolane and 2-benzyl-1,3-oxathiolane have been prepared and the latter compound has been oxidised to the corresponding sulfoxide, whose structure and conformation is examined by ¹H NMR, and to the sulfone whose X-ray structure is determined. 2-Benzylidene-1,3-oxathiolane is also prepared and the behaviour of the three S-oxidised oxathiolane derivatives upon FVP is examined. While extrusion of SO_n to give ethene and a carbonyl compound predominates in all three cases, the sulfoxide also gives bis(2-hydroxyethyl) disulfide, most likely formed via thiirane S-oxide and 1,2-oxathietane.