Due to their ready accessibility') and the almost inexhaustible prodigality of addition reactions to the enediol double bond3), hydroxyglycal esters of type I have proven to be key intermediates for the preparation of a large variety of versatile chiral building blocks 4), particularly suited for the synthesis of non-carbohydrate natural products in enantiomerically pure form4,'). Similar synthetic potential attends to the 3-0x0 analogues of hydroxyglycal esters, i.e. acylated dihydropyranones of type 11, which in view of the carbonyl-engendered reasonance stabilization (cf. arrows in 11) and the lack of a displaceable allylic acyloxy group are apt to undergo addition reactions with high regio-and diastereoselectivity .
OR
84R o + J r , Ro7$yR R'Although a sizable number of dihydropyranones of type 11 have been recorded in literatureinvariably prepared from D-glucose or its disaccharides and hence of D-erythroor (R,R)-configurationtheir accessibility is all but satisfactory. The free enediolone 1, for example, is a capricious, instable compound which has been obtained in low yield by base-induced elimination of methanol from methyl P-D-ribohexosid-3-ulose6), whereas the acetyl derivatives 2 and 3 evolved from studies on the base-catalyzed degradation of carbohydrates',') comprising acetylated hexos-2-uloses as key intermediates and a multistep sequence from D-glucose clearly inadequate for their obtention on a preparative scale.Subsequent developments of alternate routes for their preparation proceeded along two veins, one making use of the facile peroxidation of hydroxyglycal esters (I) to peracylglycos-2-uloses9) and their ready conversion into 2,3-enediol esters by acetylation" in which the anomeric substituent is eliminated with concomitant liberation of the carbonyl function simply by treatment with A1Cl3 lo). This approach led
A practical, large‐scale adaptable four‐step procedure is given for the conversion of D‐glucose (I) into pyranoid enediolone esters with (R,R)‐configuration in contiguous chiral centers such as (IV).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.