Manganese(III)-based intramolecular macrocyclization of 3,3-diphenyl-2-propenyloxyoligomethylene 3-oxobutanoates

The reaction of 3,3-diphenyl-2-propenyloxytetramethylene 3-oxobutanoate (14) with manganese(III) acetate dihydrate in boiling acetic acid caused the oxidative intramolecular radical cyclization to produce 13-methyl-11,11-diphenyl-3,8,12-trioxabicyclo[8.3.0]tridec-13-en-2-one (24) in 94% yield. A similar oxidation of the 3,3-diphenyl-2-propenyloxyoligomethylene 3-oxobutanoates (1n: n=2, 3, 6, 8) gave the corresponding macrolides 2n (n=2, 3, 6, 8) in moderate to good yields. A 17-membered crown ether-type macrolide 211 was also obtained in 80% yield by the intramolacular radical cyclization of the oxaethylene-tethered 3-oxobutanoate (111). The structure of the macrolides 2n (n=2, 3, 4, 6, 11) has been corroborated by an X-ray crystal structure analysis.