REGIOSELECTIVE PALLADIUM-CATALYZED TANDEM ALPHA-ARYLATION ISOMERIZATION OF CYCLIC ENAMIDES

Palladium-catalyzed reactions of aryl iodides with the cyclic enamides 1-(methoxycarbonyl)-1,4,5,6-tetrahydropyridine (1), 1-formyl-1,4,5,6-tetrahydropyridine (2), and 1-formyl-2-pyrroline (3) result in regioselective a-arylation, with concomitant isomerization of the double bond into conjugation with the nitrogen atom. The new enamides 1-(methoxycarbonyl)-2-aryl-1,2,3,4-tetrahydropyridines (4), l-formyl-2-aryl-1,2,3,4-tetrahydropyridines(5), and l-formyl-5-phenyl-2-pyrroline (6a) were isolated in various yields. The migration of the double bond is affected (a) by an amino group in the ortho position of the aryl iodide; (b) by the presence of silver salts; and (c) partly by a 4-methyl group in the tetrahydropyridine ring. In these cases the allylic compounds 2-aryl-1,2,5,6-tetrahydropyridines (10a,b and 13) are formed. © 1990, American Chemical Society. All rights reserved.