Photoisomerization of Vinylboranes with an Organocatalyst

Molloy and Gilmour et al. have reported a new photoisomerization of vinylboranes.¹⁾ According to their report, vinylboranes can quickly isomerize in the presence of thioxanthone as a photocatalyst to give the corresponding compounds in high yields by irradiation under visible light. In this reaction, both the borane moiety and carbonyl group are necessary and is found that the isomerization seldom proceeds in absence of each other thus indicates an olefin-selective isomerization is possible. The given products can be utilized in Suzuki-Miyaura cross coupling and the stereoselective Diels-Alder reaction, and are applicable to the synthesis of regiometric isomers of retinoic acid. The photoisomerization of olefins has been already reported,²⁾ but the substrates were limited to styrene derivatives. However, the reaction has an advantage of wide substrate versatility with only exception of presence of a borane moiety and a carbonyl group.