The photochemistry of 2-pyridylacetate methides and their pyrimidine analogues

Abstract

Photolysis of 1-benzyl-2-imino-1,2-dihydropyrimidine (IIIa) was found to afford 2-benzylaminopyrimidine (IVa), a Dimroth rearrangement product, but the 1-methyl analogue (IIIb) does not give 2-methylaminopyrimidine (IVb). A similar photochemical 1,3-alkyl migration was observed for 1-alkyl-2-ethoxycarbonylmethylene-1,2-dihydropyridines (VI) giving ethyl α-alkyl-2-pyridylacetates (VII). For example, the 1 -benzyl compound (VIa) gives (VIIa) readily, but the 1 -methyl counterpart (VIc) yields (VIIc) inefficiently. A mechanism involving homolytic cleavage and recombination is postulated for the rearrangement.