[摘要]:A single-step catalytic ring-expansion approach from 4-oxoazetidine-2-carbaldehydes to protected enantiopure 5-cyano-3,4-dihydroxypyrrolidin-2-ones has been achieved by the use of I2 in the presence of Me3CSiMe2CN. Interestingly, the catalyst directs the reaction toward the selective rearrangement of the b-lactam nucleus rather than cyanohydrin formation.