Synthesis of thiepen and thiocin derivatives via ring enlargement

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Abstract
A general method has been developed for the synthesis of two novel classes of heterocyclic compounds, 2,3‐(or 2,7)‐dihydrothiepins and 2,3‐dihydro‐8H‐thiocins. It comprises the cycloaddition of enamine derivatives of tetrahydro‐thiophen‐3‐ones or 4‐thiacyclohexanone to activated acetylenes, e.g. dimethyl acetylenedicarboxylate, yielding bicyclic adducts, which upon thermal ring opening of the cyclobutene moiety afford the thiepin and thiocin derivatives.The enamine group in these cyclic dienamines can be hydrolysed to give stabilized enols and/or their tautomeric ketones.Peracid oxidation of the sulfur atom in the dihydrothiepins or dihydro‐2H‐thiocins produces the corresponding 1‐oxides or 1,1‐dioxides.

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