The reaction of cinchonidine (cinchonine)-derived ammonium salts with nitroolefins in the presence of Cs2CO3 to afford optically active isoxazolineN-oxides with excellent ee and high de values has been developed.
A protocol for the synthesis of isoxazolineN-oxides and its application in the formal synthesis of dehydroclausenamide are described. Sulfonium salt 1 reacts with substituted nitroalkenes smoothly to generate isoxazolineN-oxides in high to excellent yields with dr higher than 99/1. Its asymmetric version has been developed by using cinchona alkaloid-derived ammonium salts 6a and 6b instead of sulfonium