King Mo Sun

Synthesis and “anomerization” of C-glycosyl compounds related to some heterocyclic natural products

Abstract Reaction of 2,3- O -isopropylidene- d -ribofuranose ( 13 ) with the stabilized Wittig reagents Ph 3 PC(Me)CO 2 Me ( 14 ) and Ph 3 PC(Me)CN ( 15 ) gave olefinic products which, upon treatment with dilute base, afforded the corresponding anhydro sugars having the β- d -anomer configuration exclusively. Treatment of these kinetic products with a strong base did not affect the ester obtained from 14 , but the nitrile from 15 gave a β-to-α-anomer ratio at equilibrium of 4:1. Reaction of 13 with Ph 3 PCHCOMe led directly to a 7:3 mixture of β- and α- d anomers, and this ratio was changed to 1:4 upon prolonged exposure to base. Treatment of 4,6- O -ethylidene- d -glucopyranose with the Wittig reagent Ph 3 PCHCOCH 2 CO 2 Et led directly to a 1:1 mixture of the anomers of the anhydro sugar in which a β-keto ester residue is attached at the (original) anomeric center. This ratio of anomeric forms could not be changed by treatment with base, but the ethylidene-protecting group could be removed, and the resulting tetrol tritylated at the primary position.

Complete stereoselectivity in the intramolecular Diels–Alder reaction of an ester derived from ‘deacetone glucose’

The intramolecular Diels–Alder reaction of the ester (3), which is readily obtainable from ‘diacetone glucose,’ gives compound (4) but under the reaction conditions sunstantial 1,3-prototropic shift occurs with the formation of (8).