Photodecarboxylation of N-Adamantyl- and N-Phenylphthalimide Dipeptide Derivatives

Abstract

New dipeptide derivatives 1 and 3 were synthesized and their reactivity in the photochemical reaction of decarboxylation was investigated. The photodecarboxylation of N-adamantyl derivatives 1a and 1b and N-phenylphthalimide derivatives 3a and 3b probably takes place from the triplet excited state. The triplet excited state of 1a, 3a and 3b was characterized by laser flash photolysis. N-phenylphthalimides 3a and 3b undergo 2-5 times more efficient photodecarboxylation than N-adamantylphthalimides 1a and 1b. The aminoacid residue (Phe or Gly) at the C-terminus of the dipeptide does not influence the photodecarboxylation efficiency. Product selectivity in the photoreactions is determined by the conformation of the molecules. N-phenylphthalimides with the separated electron donor (carboxylate) and acceptor moiety (phthalimide) give only simple decarboxylation products, whereas N-adamantyl derivatives also give cyclization products.