The Pyranoside Ring as a Nucleophile in Aldol Condensations

The enolate derived from a 2-deoxy-3-keto-hexopyranoside undergoes aldol condensations in high yields. With respect to the newly formed bond, the orientation at C2 is always axial, indicating that the pyranoside moiety exerts excellent stereoselectivity at that center. Although the enolate appears to induce little facial selectivity in the aldehyde partner, a-substituents in the latter have a profound effect, the product being formed according to the Felkin-Anh model. Thus, the acetonides of Rand Sglyceraldehydes react to give syn and anti products, respectively, with complete stereoselectivity in each case. © 1987, American Chemical Society. All rights reserved.

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Author Andrew T. McPhail Chemistry