Complete memory of chirality upon photodecarboxylation of mesityl alkanoate to mesitylalkane: theoretical and experimental evidence for cheletropic decarboxylation via a spiro-lactonic transition state

The photodecarboxylation of chiral mesityl alkanoate to mesitylalkane has been studied experimentally/theoretically, and it has been found that the photodecarboxylation proceeds to give the product in > 99% enantiomeric excesses under a variety of conditions, indicating no involvement of any radical intermediates, but that the reaction proceeds through the concerted cheletropic extrusion of CO2 from the energetically less-favored s-cis conformation.