Synthesis of optically pure fluorosubstituted isoxazolidines by 1,3-dipolar cycloaddition of nitrones to chiral methyl enol ethers of 3-fluoro-1-sulphinyl-2-propanones
作者:Pierfrancesco Bravo、Luca Broché、Alessandra Farina、Giovanni Fronza、Stefano Valdo Meille、Annamaria Merli
DOI:10.1016/s0957-4166(00)80057-9
日期:1993.10
Optically pure enol ether 4 undergoes 1,3-dipolar cycloaddition, with C,N-diphenylnitrone 5 to give the fluorosubstituted isoxazolidine 6 in a fully regio- and diastereoselective manner. The absolute configuration of 6 has been established by X-ray analysis. When changing the nitrone and/or the fluoro substitution pattern in compounds similar to 4, the same reactivity is observed.
Isoxazolidine nucleosides bearing an hydroxyl group at C3, have been prepared in only three steps, with overall high yields. The synthetic approach is based on the 1,3-dipolar cycloaddition of 3-carboxyalkyl- or acylnitrones to vinyl acetate, followed by condensation with silylated thymine or 5-fluorouracil and NaBH4 reduction.