Photosensitized [2 + 2]-Cycloadditions of Dioxaborole: Reactivity Enabled by Boron Ring Constraint Strategy.

A strategy to achieve photosensitized [2 + 2] cycloadditions by means of temporary ring constraint is reported. Specifically, a dioxaborole is prepared that undergoes [2 + 2] cycloadditions with a wide variety of alkenes. This strategy overcomes some challenges with the cycloaddition of acyclic substrates. The products can be easily transformed into cyclobutyl diols or 1,4-dicarbonyl compounds; the latter represents a formal alkene vicinal diacylation. The synthetic utility of this method is shown in the synthesis of valuable heterocycles and biatriosporin D.