Unsaturated sugar δ-lactones react with a mixture of hydroxylamine and formaldehyde (formaldoxime) either via stepwise process to produce the 1-aza-3,9-dioxa-8-oxo-bicyclo(4.3.0)nonan derivative, or via 1,3-dipolar cycloaddition of the nitrone form affording the 8-aza-3,7-dioxa-2-oxo-bicyclo(4.3.0)nonan derivative.
1,3-Dipolar cycloaddition of nitrone 7 to α,β-unsaturatedδ-lactones: non-chiral 2, racemic mixture 3/3ent, d-glycero3 and d-threo15 proceeds with high stereoselectivity in the case of 2 and 15, and with a significant kinetic resolution in the case of the racemate 3/3ent. The endo approach of reactants was not observed. CD-spectroscopy proved an attractive tool for determination of the absolute configuration
1,3-Dipolar cycloadditions of the nitrone 1 to alpha,beta-unsaturated delta-lactones: non-chiral 13, racemic mixture 3/4, D-glycero 3, and L-glycero 4 proceed with high stereoselectivity in the cases of 13 and 3 and a significant kinetic resolution in the case of the racemate 3/4. The exo approach to the re-re sides of the lactones predominates. (C) 2000 Elsevier Science Ltd. All rights reserved.
An approach to β-lactams from α,β-unsaturated sugar δ-lactones