Diastereoselective syntheses of pyrazolyl isoxazolidines via 1,3-dipolar cycloaddition

Synthesis of novel 2,3,4,5-tetrasubstituted isoxazolidine and 2,3,5-trisubstituted isoxazolidine by 1,3-dipolar cycloaddition of nitrones with electron-deficient and electron-rich olefins is described. 1,3-Dipolar cycloaddition of nitrones with β-nitrostyrene, gives exclusively endo-diastereoisomer of isoxazolidine and with ethyl vinyl ether, gives exo-diastereoisomer of isoxazolidine with de >95%. The stereochemistry of the products were assigned using extensive NMR studies.