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A general synthesis of symmetrical bi(cycloalkylidene)s is reported, involving successive reaction of an azine with hydrogen sulphide to give a 1,3,4-thiadiazolidine, oxidation to a Δ3-1,3,4-thiadiazoline, pyrolysis to a thiiran, and desulphurisation. The stereochemistry of the products and intermediates was elucidated by 1H n.m.r. spectroscopy with reference to the Woodward–Hoffmann rules and to conformation theory. The intermediate thiadiazolidines may also be prepared by direct condensation of a cycloalkanone with hydrazine and hydrogen sulphide, with different stereochemical consequences.A novel synthesis of mixed azines by oxidation of carboxyhydrazones with lead dioxide is described. Combined with the above process, this constitutes a general synthesis of unsymmetrical bicycloalkylidenes. This method has been used to prepare 3,17-disubstituted Δ9-6,7-dinor-5,8-secoestrenes. The stereochemistry at C-3 in these olefins and in the intermediate episulphides was assigned by correlation with known compounds, and the orientation of the sulphur atom in the episulphides was elucidated by 1H n.m.r. spectroscopy with reference to conformation theory and the Woodward–Hoffmann rules. Unexplained differences in the 1H n.m.r. spectra of secosteroidal epoxides and episulphides are described.
Humphreys et al. (1978) studied this question.