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.