1,3-DIPOLAR CYCLOADDITIONS OF A CHIRAL OXAZOLIDINONE WITH NITRONES AND NITRILE OXIDES

The 1,3-dipolar cycloaddition reactions of the chiral oxazolidinone (1 ) and nitrones are highly regioselective and only 5,5-disubstituted is oxazolidine adducts are formed. These reactions occur under equilibrat ing conditions to give the more stable adducts that result from additi on to the exocyclic methylene of (1) from the sterically more hindered pi-face. The endo adducts are generally thermodynamically favoured. I n one case the novel azetidine (21) was formed from the treatment of t he adduct (4a) with palladium hydroxide on carbon under a hydrogen atm osphere. The major adducts from the reaction of (1) and nitrile oxides (16a,b) had the expected stereochemistry, addition of the 1,3-dipole having occurred from the less hindered pi-face of the exocyclic methyl ene of (1). The stereochemistry of many of these products has been elu cidated by single-crystal X-ray structural determinations.