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Cycloadditions 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Protecting-group-free synthesis of glycoconjugates. • Cycloadditions under Microwave activation. • Strong antifungal isoxazolidines obtained in good yields and few steps. • Potential use as crop-protecting agents. A straightforward synthesis of carbohydrate templated isoxazolidines is described, by reaction of unprotected glycosylhydroxylamines (operating as 1,3-dipoles) with methyl acrylate using microwave activation. Rhamno - and erythro -isoxazolidines are recognized by plant cells, resulting in a strong ROS-production as a plant immune response, and exert a high antifungal activity against Botrytis cinerea. [ABSTRACT FROM AUTHOR]

Abstract: A convenient approach to the construction of dihydroxylated unsaturated azepanes featuring a functional group (ethoxycarbonyl)methyl or (cyano)methyl at C-2 was achieved from a pent-4-enal synthon obtained in four steps from d-xylose. The key step of the sequence relied on the conjugate addition of allylamine to α,β-unsaturated ester or nitrile, prepared by Wadsworth–Emmons olefination. Subsequent RCM afforded the target unsaturated azepanes. [Copyright &y& Elsevier]

Key steps in the synthesis of azepanes (VIII) and (X), which are of interest as glycosidase inhibitors, are the conjugate addition of allylamine to the precursor (III) and final ring-closing metathesis with the pure diastereomers (VII) and (IX). [ABSTRACT FROM AUTHOR]