Photodecarboxylation of Adamantane Amino Acids Activated by Phthalimide

Abstract

Adamantane α‐, β‐, and δ‐amino acids activated by phthalimide (i.e., 3–6) were synthesized, and their photochemical reactivities were investigated. Amino acid derivatives 3–6 underwent a photoinduced electron transfer (PET) and decarboxylation reaction sequence, most probably through a triplet excited state. The decarboxylations of the β‐amino acid derivatives were succeeded by cyclization reactions that afforded complex polycyclic molecules with potential biological interest. The adamantyl radical that is produced by the photoinduced decarboxylation could be trapped by alkenes or oxygen to deliver adducts or alcohols, respectively. The photodecarboxylation process was shown to be more efficient under acetone sensitization conditions (with quantum yields, Φ = 0.02–0.5) than upon direct excitation, and the reactivity was dependent on the chain length (intramolecular distance) between the electron donor (carboxylate) and acceptor (phthalimide in the triplet excited state) of the derivative. The formation of different radicals, that is, the 1‐ or 2‐adamantyl intermediate, probably does not affect the overall rate of the decarboxylation This current report provides a better understanding of photodecarboxylation and the rational design of molecular systems to undergo photoinduced decarboxylation and cyclization reactions.