Regioselective 1,4-addition of ammonia to 1-arylalka-1,3-dienes and 1-aryl-4-phenylbuta-1,3-dienes by photoinduced electron transfer

Abstract

The photoamination of 1-arylalka-1,3-dienes 1a–f and 1-aryl-4-phenylbuta-1,3-dienes 1g–k with NH₃ in the presence of p-dicyanobenzene (DCB) gives 4-amino-1-arylalk-2-enes 2a–f and 1-amino-1,4-diarylbut-2-enes 2g–k, respectively. The photoamination proceeds by nucleophilic addition of NH₃ to the cation radicals of 1^+˙ generated by photoinduced electron transfer to DCB. The regiochemistry of 2 is related to the distribution of the positive charge in 1^+˙ calculated by the PM3-UHF/RHF method, the stability of the aminated radicals formed by the addition of NH₃ to 1^+˙ and the stability of the aminated anion formed by the reduction of the aminated radicals by DCB^-˙. The stabilities of these intermediates are estimated by the calculation of the heat of formation by the PM3-UHF/RHF method. Distributions of the positive charge in 1^+˙ and the stabilities of the aminated anion show a good agreement with the product analysis.