- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and β-Pyrufuran, a Synthesis of Tri-O-methylleprolomin and its Demethylation
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes.The scope and utility of this reaction are explored with examples drawn from derivatives of benzene, naphtalene, 9,10-dihydrophenanthrene and dibenzofuran.The method is applied to the synthesis of the phytoalexins α- (56) and β-pyrofuran (58) (1,3,4-trimethoxydibenzofuran-2-ol and 1,2,4-trimethoxydibenzofuran-3-ol).A synthesis of tri-O-methylleprolomin (61), a derivative of the unusual lichen metabolite leprolomin (60), is described and its demethylation with boron trichloride is studied.
- Carvalho, Christopher F.,Russo, Albert V.,Sargent, Melvyn V.
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p. 777 - 792
(2007/10/02)
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- Isolation and Structure Determination of &γ-Pyrufuran, A Third Induced Antifungal Dibenzofuran from the Wood of Pyrus communis L. infected with Chondrostereum purpureum (Pers. ex Fr.) Pouzar
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The induced antifungal compound γ-pyrufuran has been isolated from the wood of perry pear trees infected with Chondrostereum purpureum (Pers. ex Fr.) Pouzar.Spectroscopic and chemical evidence indicate that the compound is one of four 1,2,3,4,7-substituted trimethoxydibenzofurandiols in which one hydroxy group occupies the 7-position.Selective reduction of the dimesylated derivative by hydrogen with a Pd-C catalyst, followed by base-catalysed hydrolysis, produced α-pyrufuran (1,3,4-trimethoxydibenzofuran-2-ol) (6), and shows γ-pyrufuran to be 1,3,4-trimethoxydibenzofuran-2,7-diol (1).
- Kemp, Malcolm S.,Burden, Raymond S.
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p. 1441 - 1443
(2007/10/02)
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- Isolation, Structure Determination, and Total Synthesis of the Dibenzofurans α- and β-Pyrufuran, New Phytoalexins from the Wood of Pyrus communis L.
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The antifungal compounds α- and β-pyrufuran have been isolated from the wood of perry pear trees infected with Chondrostereum purpureum (Pers. ex Fr.) Pouzar, the causative fungus of silver leaf disease.Spectroscopic and chemical evidence show that the compounds are 1,2,3,4-substituted trimethoxydibenzofuranols.Three of the four possible positional isomers, compounds (11), (12), and (13), have been synthesized by cyclisation of the corresponding trimethoxydiphenyl ethers using palladium (II) acetate, followed by oxidation of the organo-lithium derivative using lithium t-butyl peroxide.The latter stage proved unsuccessful in the attempted synthesis of 2,3,4-trimethoxydibenzofuran-1-ol (10).Comparison of spectroscopic and chromatographic properties of the natural products and synthesized compounds show α-pyrufuran and β-pyrufuran to be 1,3,4-trimethoxydibenzofuran-2-ol (11) and 1,2,4-trimethoxydibenzofuran-3-ol (12), respectively.
- Kemp, Malcolm S.,Burden, Raymond S.,Loeffler, R. S. Thomas
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p. 2267 - 2272
(2007/10/02)
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