New procedures for the synthesis of 3(2H)-furanones and 4-alkoxy-2(5H)-furanones are reported. Reaction of ketones with the lithium salt of propynal diethyl acetal, followed by treatment of the resulting 4-hydroxy-2-alkynal diethyl acetals with sulfuric acid–methanol, gave 2,2-disubstituted 3(2H)-furanones. The action of a polymer reagent Hg/Nafion-H upon 4–hydroxy-2-alkynones produced 2,2,5-trisubstituted
A newsyntheticmethod of 3-acyltetronic acidderivatives from the corresponding 3-bromo compound via lithiation with n-BuLi followed either by acylation with acid chloride or better by first reacting with aldehyde and then subsequent oxidation with active MnO2 is described. A revised structure for aspertetronin A(gregatin A) was presented based on the synthesis of the proposed structure and spectral
Refined Protocols for the Preparation of 3-Alkoxy-2,5-dihydrofurans, Allylic Oxidation to β-Alkoxybutenolides and Short Synthesis of (±)-Annularin H
作者:Hans-Ulrich Reissig、Malte Brasholz
DOI:10.1055/s-2007-977456
日期:——
The 5- ENDO cyclization of α-allenyl alcohols derived from carbonyl compounds and lithiated alkoxyallenes was reinvestigated by comparing the known reagents KO T-Bu, AgNO 3 or AgBF 4 with the reagent system AuCl/pyridine. A variety of 3-alkoxy-2,5-dihydrofurans 4 was efficiently prepared, in some cases with high diastereoselectivity. These product compounds were -subjected to manganese(III)-catalyzed
通过将已知试剂 KO T-Bu、AgNO 3 或 AgBF 4 与试剂系统 AuCl/吡啶进行比较,重新研究了衍生自羰基化合物和锂化烷氧基丙二烯的 α-丙二烯醇的 5-ENDO 环化。有效地制备了多种 3-烷氧基-2,5-二氢呋喃 4,在某些情况下具有高非对映选择性。这些产物化合物经过锰 (III) 催化的烯丙基氧化,得到中等至良好产率的 β-烷氧基丁烯内酯。这些新调整的方法的组合允许 (±)-annularin H 的简洁和简短的合成。
3-Alkoxy-2,5-dihydrofurans by Gold-Catalyzed Allenyl Cyclizations and Their Transformation into 1,4-Dicarbonyl Compounds, Cyclopentenones, and Butenolides
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 β-alkoxy butenolides by a manganese(III) acetatecatalyzedradicaloxidation with tert-butyl hydroperoxide, or transformed
β- and α-lithiaton of methyl β-methoxyacrylate: efficient synthesis of α,γ-substituted methyl tetronates - structure of aspertetronins and gregatins
作者:Okiko Miyata、Richard R. Schmidt
DOI:10.1016/s0040-4039(00)86743-x
日期:1982.1
Methyl β-methoxyacrylate () can be lithiated successively in β- and α-positions. Reaction with two electrophiles (at first a carbonyl compound) leads to α, γ-substituted methyl tetronates in a two step synthesis. Application of this method to the synthesis of methyl tetronate whose structure was assigned as that of gregatin B indicates that the gregatins and aspertetronins have the isomeric structures