The synthesis and structure of new vinylogous carbamates of sparteine

Synthesis of new (E)-(-)-[2-methyl (2), ethyl (3), isopropyl (4), benzyl (5) and phenyl (6)] carbonylmethylideno-17-oxosparteine by the Eschenmoser coupling reaction has been described. Stereochemistry of these compounds has been determined by 13C and 1H NMR and that of compound 2 additionally by X-ray analysis. The Haasnoot equation has been used to determine the HCCH dihedral angle in (E)-(-)-2-methyl-(methylcarbonylomethylideno)-17-oxosparteine on the basis of NMR spectroscopy.