UNUSUAL REACTIVITY OF (VINYLIMINO)PHOSPHORANES AND THEIR UTILITY IN THE PREPARATION OF PYRIDINE AND DIHYDROPYRIDINE DERIVATIVES

New reactions of (vinylimino)phosphoranes with aldehydes involving an initial nucleophilic attack of the beta-carbon atom of the vinyl side chain on the carbonyl carbon atom are reported. Iminophosphorane 4 der ived from ethyl beta-azidoacrylate reacts with substituted cinnamyl al dehydes to give a mixture of 2-arylpyridine and 4-styryldihydropyridin e derivatives, whereas the reaction with substituted benzaldehydes pro vides 4-aryldihydropyridine derivatives. However, the iminophosphorane 16 derived from the diethyl azidofumarate reacts with cinnamyl aldehy des through the expected aza-Wittig fashion to give 4-arylpyridine der ivatives after dehydrogenation of the resulting dihydropyridine.