Photoaddition of Allylic and Benzylic Groups to 1, 1-Dicyanoethenes Bearing Heterocyclic Substituents by Use of Organic Stannanes

Abstract

Irradiation of an aqueous acetonitrile solution containing 1, 1-dicyano-2-(2-furyl)ethene and allyltributylstannane in the presence of phenanthrene gave regioselectively 5, 5-dicyano-4-(2 fury1)-1-pentene. Similar photoaddition reactions occurred upon irradiation of mixtures of 2-(2-furyl- or 2-thienyl)-substituted 1, 1-dicyanoethene derivatives and allylic and benzyli c stannanes in the presence of phenanthrene, affording the corresponding allylated or benzylated products in good yields. In these photoreactions, the allylic or benzylic groups were introduced into the β-carbon and hydrogen into the α-carbon to the cyano function of 1, 1-dicyanoethene derivatives with high regioselectivity. Such photoallylation reactions did not occur when allylic silanes were used in place of allylic stannanes. No reaction took place by irradiation in nonpolar solvents and also by refluxing the reaction mixture in the dark. The electron transfer mechanism is proposed for the photoreactions. The reactions involve coupling between 1, 1-dicyanoethene radical anions and allylic or benzylic radicals which are produced from the stannane radical cations.