Mechanism of the photoreaction between 1,4-dicyanonaphthalene and benzylic donors

Abstract

The reaction of 1,4-dicyanonaphthalene (DCN) with ethylbenzene, propylbenzene, and α-methylbenzyltrimethylsilane has been investigated and compared with previous results obtained using other benzylic donors. The relative yield of the different types of reaction observed, (a) substitution of a cyano group to yield naphthalenes 2, (b) addition to yield the dihydronaphthalenes 3 and 4, and (c) addition with cyclization to yield the tetracyclic derivatives 5 as well as the diastereoisomeric distribution within each type of product, show that these reactions occur by different paths, all initiated by electron transfer, involving respectively cleavage of the free radical cation [for case (a)], detachment of a proton or a silyI cation and (probably concerted) addition to DCN˙^–[for case (b)]. and proton transfer within the initial radical ion pair [for case (c)].