Synthesis of 5-Fluoroalkyl Isoxazolidines via 1,3-Dipolar Cycloaddition of Ethyl 2-Hydropolyfluoroalk-2- enoates with Nitrones

Dipolar cycloaddition reactions of ethyl 2-hydropolyfluoroalk-2-enoates (1) with some nitrones were de-scribed. The reaction of 3,4-dihydroisoquinoline N-oxide (2) with 1 took place readily in methylene chloride at room temperature to give the corresponding 5-fluoroalkylisoxazolidines regioselectively as a mixture of two di-astereoisomers (trans and cis) in high yields, while longer reaction time and higher temperature were needed in the case of non-cyclic nitrones. Under similar conditions the reaction of quinoline N-oxide (14) with 1 did not give the expected adducts and a ring-opening product was obtained.