A Novel Photochemical Cycloaddition of 1-Cyanonaphthalene to Substituted Pyridines

Abstract

The photochemical reaction of 1-cyanonaphthalene (1-CNNap) with substituted pyridine was studied. Irradiation of a benzene solution of 1-CNNap (0.02 M) in the presence of 3-cyano-2-methoxypyridine (0.02 M) gave a 1:1 adduct in 24% yield and the pyridine dimer in 56% yield, when the reaction conversion reached 32%. Photoaddition of 1-CNNap with 3-cyano-2-methoxy-6-methylpyridine, 3-cyano-4,6-dimethyl-2-methoxypyridine, or 3-cyano-2,6-dimethoxypyridine was also successful, and the corresponding adducts were isolated in 41%, 75%, and 98% yield, respectively. The structure was established by X-ray structural analysis. The postulated mechanism initiated by 2π+2π photocycloaddition between the C3−C4 position of 1-CNNap and the C2−C3 position of the pyridine was supported by Frontier-MO calculations using the PM3 Hamiltonian contained within the MOPAC program. The naphthalene−pyridine adducts were stable at room temperature; however, pyrolysis of the adduct gave a 1,3-sigmatropic rearrangement product, quantitat...