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.

Photogeneration of Amines from α-Keto Carbamates: Photochemical Studies

“…While the mechanism of amine photogeneration from 3‘,5‘-dimethoxybenzoin carbamates is not the primary focus of this work, it certainly merits some discussion. Since the photocleavage mechanism of benzyl esters, carbonates, and carbamates are similar, details of the mechanism of amine photogeneration from benzoin carbamates may, in part, be elucidated from prior mechanistic work on photocyclization of substituted benzoins. In the case of benzoin phosphate, photocleavage is quenched by common triplet quenchers indicating that the reaction proceeds via the triplet manifold .…”