Direct Access to Unnatural Cyclobutane α-Amino Acids through Visible Light Catalyzed [2+2]-Cycloaddition.

In this work, we report the first selective, photocatalyzed [2+2]-cycloaddition of dehydroamino acids with styrene-type olefins. This simple, mild, and scalable approach relies on the use of the triplet energy transfer catalyst [Ir(dFCF 3 ppy 2 )dtbpy]PF 6 under visible light irradiation and provides fast access to value-added substituted strained cyclobutane α-amino acid derivatives.