One-Pot Stereoselective Synthesis and Structural Study of 1-Methylthio- 2-azabuta-1,3-diene-4-carbonitriles.

The methylation of the carbanion resulting from addition of thioamides to methoxymethylene compounds 1 or ketene dithioacetals 2 affords two series of 1-methylthio-2-azabuta-1,3-diene-4-carbonitriles 5 or 6. The IR, MS and 1H and 13C NMR spectral properties are reported. X-Ray crystallographic analyses established the E stereochemistry of the C–N double bond in all cases studied. Isomerization of the C–N double bond was achieved by treatment of the 2-aza dienes 5a and 6a with sodium methanethiolate in propan-2-ol at room temperature.