Synthesis of novel O-acylated-D-ribono-1,5-lactones and structural assignment supported by conventional NOESY-NMR and x-ray analysis (original) (raw)
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The syntheses of the chiral ~,13-unsaturated lactones (+)-5, (-)-6, (+)-8, (+)-9, and (+)-10 have been efficiently achieved from readily available starting materials. The lactone (+)-5 has been synthesized in 7 steps from (R,R)-dimethyl tartrate (38-43% overall yield). The use of (+)-5 in formal syntheses of natural (+)-asperlin 4 and advanced intermediates for (+)-olguine 2 are also reported. The lactone (-)-6 has been prepared in 5 steps from (R)-malic acid (44-50% overall yield). It can be a useful precursor for the syntheses of branched chain and deoxy nucleoside analogues. The preparation of (-)-6 constitues formal syntheses of natural (+)-eldanolide 53 and the (+)-Geissman-Waiss lactone 54 (an intermediate for the syntheses of a variety of pyrrolizidine alkaloids). The lactones (+)-8, (+)-9 and (+)-10 have been synthesized from 3,4-di-O-acetyI-Lrhamnal 58. The highly diastereoselective transformations of (+)-9 and (+)-10, through sequential conjugate nucleophilic addition and enolate reaction, into densely functionalized chiral y-lactones 12 are also reported.
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A practical synthesis of 2-deoxy-L-ribose from L-arabinose depends on the efficient reduction by iodide of a triflate a to a lactone. The X-ray crystal structure of 3,4-O-isopropylidene-L-arabinono-1,5-lactone is reported.
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The exploration of β-lactone reactivity and transformations has continued since the first synthesis of these strained heterocycles by Einhorn in 1883. The principal reactivity modes of β-lactones include nucleophilic addition resulting in either acyl C2-O1 or alkyl C4-O1 cleavage, rearrangement leading to ring expansion, decarboxylation, and electrophilic reactions of β-lactone enolates.
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Acylation of ammonium 3-deoxy-n-D-manno-Z-octulopyranosonate (la) leads to the formation of peracetylated 3-deoxy-a-D-manno-2-octulopyranosono-1,5-lactones (3a,b). The proposed structures were confirmed by independent syntheses. The 1,7-lactone was not formed even when only OH-7 was available for lactonisation.
Tetrahedron Letters, 2009
We present here the application of Grubbs' 2nd generation catalyst for the ring-closing metathesis of electron-deficient a,b-unsaturated amides and esters leading to the synthesis of enantiopure azepinone and oxepinone derivatives on a carbohydrate glycoside scaffold. The relative stereochemistries of the compounds obtained were corroborated by X-ray crystallography, 1 H NMR or deduced based on previously reported results. These compounds are designed as precursors of new polyhydroxylated heteroannulated sugars with potential biological activity.
β-Lactones: Intermediates for Natural Product Total Synthesis and New Transformations
HETEROCYCLES, 2004
The exploration of β-lactone reactivity and transformations has continued since the first synthesis of these strained heterocycles by Einhorn in 1883. The principal reactivity modes of β-lactones include nucleophilic addition resulting in either acyl C2-O1 or alkyl C4-O1 cleavage, rearrangement leading to ring expansion, decarboxylation, and electrophilic reactions of β-lactone enolates.