The photochemistry of 1-naphthylmethyl carbonates and carbamates

Abstract

The photochemistry in methanol of 1-naphthylmethyl phenyl carbonate (3) and 1-naphthylmethyl benzyl carbonate (4) has been studied. Products resulting from both the 1-naphthylmethyl cation and the 1-naphthylmethyl radical are obtained for 3, but only from the cation for 4. Similar results were obtained for the corresponding 1-naphthylmethyl derivatives 5 and 6 of N-phenyl and N-benzyl carbamic acids. The product yields for all four compounds can be explained by a mechanism of initial homolytic cleavage of the 1-naphthylmethyl carbon–oxygen bond from the excited singlet state. The radical pair generated then partitions between the two pathways: electron transfer to form the ion pair or decarboxylation. For PhO-CO-O• and PhNH-CO-O•, decarboxylation is rapid and competitive with electron transfer. For PhCH2O-CO-O• and PhCH2NH-CO-O•, decarboxylation is slower, electron transfer dominates, and only products from the ion pair are obtained.