Abstract
An enantioselective formal synthesis of (+)-dodoneine is described using the Sharpless asymmetric dihydroxylation and regioselective nucleophilic opening of cyclic sulfate as the key steps.
Highlights
Dodoneine 1, [(R)-6-[(S)-2-hydroxy-4-(4-hydroxyphenyl)butyl]-5,6-dihydropyran-2-one], is a recently isolated α,β-unsaturated δ-lactone from the methanolic extract of a plant hemi parasite, Tapinanthus dodoneifolius DC Danser found on a sheanut tree in Loumbila, West Africa.[1]
The synthesis approaches described till in the literature for dodoneine 1 involve 1) enantioselective addition of allyl metal reagents to aldehydes, followed by Grubbs ring closing metathesis3 2) Horner-Wadsworth-Emmons olefination and Crimmins aldol approach[4] and 3) Sharpless asymmetric epoxidation followed by 1,3-syn diasteroselective reduction and Grubbs ring closing metathesis.[5]
As part of our research work aimed at developing enantioselective syntheses of naturally occurring lactones, the Sharpless asymmetric dihydroxylation and subsequent transformation of the diols formed via cyclic sulfites/ sulfates were envisaged as powerful tools offering considerable opportunities for synthetic manipulations.[6]
Summary
Dodoneine 1, [(R)-6-[(S)-2-hydroxy-4-(4-hydroxyphenyl)butyl]-5,6-dihydropyran-2-one], is a recently isolated α,β-unsaturated δ-lactone from the methanolic extract of a plant hemi parasite, Tapinanthus dodoneifolius DC Danser ( known as African mistletoe) found on a sheanut tree in Loumbila, West Africa.[1]. Hydrolysis (with catalytic amount of sulfuric acid and water) of intermediate sulfate ester, obtained from cyclic sulfate 3 after treatment with sodium borohydride in DMF at 25 oC, was sluggish and gave the desired product alcohol 10 in low yields (
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