Enantioselective Synthesis and Photoreactivity of a Diazirinyl-substituted (R)-beta-Phenylalanine

摘要

The first enantioselective synthesis of a photoreactive (R)-beta-phenylalanine is described. In the key step, m-diazirinyl-substituted benzaldehyde is converted to a chiral sulfinimine in a Ti(OEt)(4)-mediated reaction, followed by diastereoselective enolate addition. The absolute configuration of photo (R)-beta-phenylalanine was confirmed by Mosher analysis. The photo amino acid proved to be thermally stable under standard laboratory conditions. Irradiation in toluene afforded cycloheptatrieneorcaradiene valence tautomers, together with carbene benzylation. Quantum-chemical calculations indicate a small triplet-singlet gap.