Copper‐Catalyzed Aerobic CC Bond Cleavage of Lactols with N‐Hydroxy Phthalimide for Synthesis of Lactones

The transformation of cyclic hemiacetals (lactols) into lactones has been achieved by Cu‐catalyzed aerobic CC bond cleavage in the presence of N ‐hydroxy phthalimide (NHPI). The present process is composed of a multistep sequence including a) formation of exo ‐cyclic enol ethers by dehydration; b) addition of phthalimide N ‐oxyl radical to the enol ethers followed by trapping of the resulting C‐radicals with molecular oxygen to form peroxy radicals; c) reductive generation of oxy radicals and subsequent β‐radical fragmentation to generate lactones.