Photochemically induced oxygenation of methylbenzenes, bibenzyls, and pinacols in the presence of naphthalene-1,4-dicarbonitrile

Abstract

The photochemical reaction of aromatic donors in oxygen-saturated solution in the presence of naphthalene-1,4-dicarbonitrile (NDN) has been investigated. Methylbenzenes (1a,b) are found to give benzaldehydes, bibenzyls (4a—d) are cleaved to benzaldehydes (or phenyl ketones) and benzyl alcohols, pinacols (7a—c) and pinacol ethers (9b, c) are likewise cleaved to carbonyl derivatives (in the latter case also to esters). The mechanism of this reaction is discussed on the basis of product distribution and quantum yield both in the absence and in the presence of oxygen, and involves electron-transfer from the donors to the NDN singlet excited state and deprotonation [for compounds (1) or (4a, b)] or carbon-carbon bond cleavage [for compounds (4c, d), (7), and (9)] of the radical cation, followed by reaction of the benzyl radicals with oxygen.