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Baeyer-Villiger oxidation of alpha-alkoxy ketones 1 provides lactone acetals 2, which react with the lithium salts of di-methyl(alkyl) phosphonates in the presence of LaCl3•2LiCl to provide cyclic enones 3 in good to excellent yields after treatment with dilute aqueous potassium carbonate. Thus, five-, six-, and seven-membered lactones are con-verted to five-, six-, and seven membered cyclic enones. The utility of this two-step ring expansion method is demonstrated in the synthesis of (±)-1-epi-xerantholide from 5-methyl-2-cyclohexen-1-one.
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In an extension of our studies on low-temperature rearrangements of 1-alkynyl ethers, we describe herein the [3,3]-sigmatropic rearrangement of in situ formed propargyl alkynyl ethers to allenyl ketenes, which furnish complex tert -butyl-(2 E ,4 Z )-dienoates 2 in good yields upon tert -butanol addition. Similarly, sigmatropic rearrangements of in situ formed propargyl lithioalkynyl ethers yield methyl-(2 Z ,4 Z )-dienoates 4 upon methanol addition or unsaturated lactones 6 upon aldehyde or ketone addition to the allenyl ynolate intermediate.more » « less
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A synthesis of hortonones A–C has been accomplished from vitamin D 2 via the Inhoffen–Lythgoe diol without the use of protective groups. Key steps in the syntheses include a TMS-diazomethane mediated regioselective homologation of the cyclohexanone ring to a cycloheptanone moiety and a sodium naphthalenide-mediated allylic alcohol transposition. It has been found that the absolute configuration of the natural hortonones is opposite that of the synthetic material prepared from vitamin D 2 .more » « less
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To explore the utility of the azinomycin B chromophore as a platform for the development of major-groove binding small molecules, we have prepared a series of 3-methoxy-5-methylnaphthalene derivatives containing diamine, triamine, and carbohydrate linker moieties. All bis- and tris-azinomycin derivatives are intercalators that display submicromolar binding affinities for calf-thymus DNA, as revealed by viscometry measurements and fluorescent intercalator displacement (FID) assays, respectively. Although the tightest binding ligand 1d ( K a = 2.42 × 10 7 M −1 ) has similar affinities for sequence diverse polynucleotides, competition binding studies with methylated phage DNA and known major and minor groove binding small molecules suggest that the tether moiety linking the naphthalene chromophores may occupy the major groove of DNA.more » « less
