1,2-Acyl transposition through photochemical skeletal rearrangement of 2,3-dihydrobenzofurans

Saturated heterocycles are commonly adorned with groups that influence their biological properties. Synthetic methods that transpose existing substituents on saturated heterocycles to multiple peripheral positions are therefore highly valuable. In this work, we report a formal 1,2-acyl transposition through the photochemical exchange of the C₂-C₃ positions of C₂-acylated dihydrobenzofurans. This strategy relies on an unusual photochemical isomerization of the dihydrobenzofuran core to a highly electrophilic spiro-cyclopropane intermediate that is then intercepted by a halide nucleophile. A variety of aryl ketones are transposed using 370-nanometer centered irradiation. Additionally, carboxylic acids, esters, and amides can be transposed using 310-nanometer centered irradiation. This work highlights the power of a skeletal rearrangement to achieve a net peripheral modification.