Additives Promote Divergent Reactivity in Photolytic Deoxygenation and Lactonization Reactions of Cobalt Alkoxycarbonyls

The formation of lactones via radical mediated C–C bond formation is a powerful but overlooked method, especially given recent interest in the conversion of alcohols to radical intermediates using photochemistry. Building on our previous work with cobalt porphyrin complexes, a carbonylation-homolysis process is described for complex unsaturated alcohols and a simple benzylic model system, leading to the production of saturated or unsaturated products. Ligands and additives are demonstrated to promote either reductive or oxidative termination, leading to divergent reactivity in different contexts. The role of cobalt hydride intermediates is also discussed, as well as the application of this strategy toward the synthesis of a lactone-containing limonoid natural product.