3-Alkoxy-2,5-dihydrofurans by Gold-Catalyzed Allenyl Cyclizations and Their Transformation into 1,4-Dicarbonyl Compounds, Cyclopentenones, and Butenolides

[摘要]：The addition of lithiated alkoxyallenes to carbonyl compounds furnishes allenyl alcohols, which undergo a highly efficient and chemoselective 5-endo-trig cyclization to 3-alkoxy-2,5-dihydrofurans catalyzed by gold(I) chloride. The dihydrofurans produced can be either oxidized to beta-alkoxy butenolides by a manganese(III) acetate catalyzed radical oxidation with tert-butyl hydroperoxide, or transformed into a, beta-unsaturated gamma-keto aldehydes by an oxidative ring cleavage using DDQ in the presence of water. Treatment of the gamma-keto aldehydes with sodium methoxide in methanol promotes a diastereoselective intramolecular aldol addition furnishing alkoxy-substituted cyclopentenone derivatives in good yield.

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