Diastereoselectivity in the Reaction of N-Glycosyl-nitrones: 1,3-Dipolar Cycloaddition and Addition of Phosphite Anion

The direction of approach of dibenzyl phosphite on the one hand and of dipolarophiles on the other hand to the spironitrone 7 was examined. The nitrone 7 was prepared from the lactone 3 . The nucleophilic addition of dibenzyl phosphite gave 8 as a single adduct (86%). Its structure was established by X-ray analysis. From the cycloaddition of methyl methacrylate, the products 9a, 9b, 11a , and 11b (83:2:7.5:7.5, 81%) were isolated. The structure of the main adduct 9a was established by an X-ray analysis of a derivative of it, and the structures of the other adducts were deduced from their NMR spectra. The cycloaddition of 7 and methyl acrylate gave the adducts 10a , 10b , 12a , 13a , 13b , and 14a (27:10:54:1:2:6, 87%). The structures of these compounds were deduced from their NMR spectra. The results are discussed in relation to prior hypothesis.