Moderate diastereoselectivities (de 2–62%) of isoxazolidine homonucleotides were observed for cycloadditions between N-methyl-C-(diethoxyphosphoryl) nitrone and N-allyl nucleobases, with trans-isoxazolidines predominating. The stereochemistry of the substituted isoxazolidines was established based on 2D NOE experiments performed for uracil-containing cycloadducts. The cis-and trans-isoxazolidine phosphonates obtained ...