Two series of nonhydroxyl isoxazolidinyl nucleoside analogues containing a trifluoromethyl group have been conveniently prepared in moderate or good yields by direct 1,3-dipolar cycloaddition. Isoxazolidines 5-7 derived from fluorinated N-vinyl nucleobases and N-alkyl-methylenenitrones were obtained with complete regiocontrol and stereocontrol and the reactions proceeded with full transfer of the dipolarophile geometry to the cycloadduct. The cycloaddition reactions of N-alkyl-trifluoromethylnitrones with N-vinyl nucleobases led with very high diastereoselectivity to cis and trans stereoisomers of isoxazolidines 13-17. Interestingly, the diastereoselectivity was strongly determined by the steric factor and definitely was dependent on the character of N-alkyl substituent in the nitrone.

通过直接的1，3-偶极环加成，以中等或良好的收率方便地制备了两个系列的含三氟甲基的非羟基异恶唑啉基核苷类似物。异恶唑烷5 - 7从氟化衍生ñ -乙烯基核碱基和ñ -烷基methylenenitrones用完整区域控制和立体控制，并与亲偶极几何的充分转移到环加成进行反应而获得。N-烷基三氟甲基亚硝基与N-乙烯基核碱基的环加成反应导致对异恶唑烷的顺式和反式立体异构体具有非常高的非对映选择性13- 17。有趣的是，非对映选择性是由空间因素强烈决定的，并且绝对取决于硝酮中N-烷基取代基的特性。