Diastereoselective transannular [2+2] photocycloaddition of ascorbic acid derivatives

Ring-closing metathesis of bis-O,O-alkenyl ascorbic acid derivatives affords cyclic ethers in good yields which can be further converted by irradiation at 254 nm into new polyoxacyclic structures according to a diastereoselective transannular [2+2] photocycloaddition.