High-Pressure Activation to Circumvent Product Degradation in the Reaction of Unprotected Glyconitrones with Alkynes

Abstract

AbstractCycloadditions of nitrones with alkynes usually occur best under heat activation. Due to the instability of the formed isoxazolines, alternative activation methods must be found. Here, hyperbaric conditions are used to transform nitrones generated from unprotected carbohydrates into the corresponding polyhydroxy-isoxazolines at room temperature. The reaction proved completely regioselective in favor of the 5-substituted 4-isoxazolines, and the products are obtained in good yields as mixtures of the two possible diastereoisomers. Further transformations into biologically valuable targets are described. The whole synthesis constitutes a very straightforward procedure for the transformation of aldoses, and is highly compatible with the principles of green chemistry.