Photochemistry of phthaloylcysteine, its methyl ester and C-unprotected S-alkyl derivatives

Abstract

N-Phthaloyl cysteine derivatives 1a-d were photochemically transformed by elimination, decarboxylation, and via electron transfer cyclization to the products 2,3,4 and 6–8. The spin selectivities of singlet and triplet pathways were investigated in acetonitrile and acetone. The excited singlets were prone to elimination and γ-H abstractions (e.g. formation of 5) whereas the triplets cyclized to thiazinoisoindoles. This behaviour can be correlated with the efficiencies of forward and return electron transfer steps versus homolytic hydrogen abstractions as examplified for the cysteine substrate 9.