Application of the silicon-tether strategy for controlling the regioselectivity and diastereoselectivity of intramolecular nitrone cycloadditions for aminopolyol synthesis

Highly regioselective and diastereoselective intramolecular chiral nitrone cycloaddition reactions with a vinyl group tethered by a silicon atom have been developed as a general method for the synthesis of stereodefined amino polyols. This strategy features a series of one-pot reactions involving (1) DIBAH reduction of the carbonyl groups of chiral α- or β-hydroxy carbonyl compounds, in which the hydroxy group is protected as diphenylvinylsilyl ethers, at -78 °C to give an aldehyde, (2) condensation of the aldehyde with N-benzylhydroxylamine to furnish nitrone (-78 °C → rt), and (3) intramolecular [3 + 2] dipolar cycloaddition reaction between the nitrone and the silicon-tethered vinyl group (rt → 70 °C, 3-15 h) to give isoxazolidine derivatives as direct precursors for amino polyols. Since the cycloaddition reaction is concerted in nature and passes through a fused-bicyclic transition state, the substituents, the nitrone substrate, and the silicon atom bias the stereochemical course of this addition, resulting in highly diastereoselective and synthetically useful transformations.