754201-06-4Relevant academic research and scientific papers
3-Alkoxy-2,5-dihydrofurans by gold-catalyzed allenyl cyclizations and their transformation into 1,4-dicarbonyl compounds, cyclopentenones, and butenolides
Brasholz, Malte,Dugovi, Branislav,Reissig, Hans-Ulrich
supporting information; experimental part, p. 3855 - 3864 (2010/12/25)
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 -alkoxy butenolides by a manganese(III) acetate catalyzed radical oxidation with tert-butyl hydroperoxide, or transformed into ,-unsaturated -keto aldehydes by an oxidative ring cleavage using DDQ in the presence of water. Treatment of the -keto aldehydes with sodium methoxide in methanol promotes a diastereoselective intramolecular aldol addition furnishing alkoxy-substituted cyclopentenone derivatives in good yield. Georg Thieme Verlag Stuttgart · New York.
Refined protocols for the preparation of 3-alkoxy-2,5-dihydrofurans, allylic oxidation to β-alkoxybutenolides and short synthesis of (±)-annularin H
Brasholz, Malte,Reissig, Hans-Ulrich
, p. 1294 - 1298 (2008/02/08)
The 5-endo cyclization of α-allenyl alcohols derived from carbonyl compounds and lithiated alkoxyallenes was reinvestigated by comparing the known reagents KOt-Bu, AgNO3 or AgBF4 with the reagent system AuCl/pyridine. A variety of 3-
Preparation of α,β-Unsaturated γ-Keto Aldehydes and New Tetronic Acid and Pyridazine Derivatives by Oxidative Transformations of Alkoxyallene-Based Dihydrofurans
Floegel, Oliver,Reissig, Hans-Ulrich
, p. 2797 - 2804 (2007/10/03)
Oxidation of 3-alkoxy-substituted dihydrofuran derivatives 6 and 11 with DDQ unexpectedly provided α,β-unsaturated γ-keto aldehydes 10 and 12. A mechanism for this new oxidative ring-cleavage is presented. Since α,β-unsaturated γ-keto aldehydes are versatile intermediates, other 3-methoxy-substituted dihydrofuran derivatives 24, 26, and 28 were prepared from lithiated methoxyallene and the corresponding aldehydes. Oxidation of dihydrofuran derivatives with DDQ and subsequent treatment with sodium chlorite furnished hydroxy-substituted tetronic acid derivatives, such as 30 and 31. Condensation of 30 with hydrazine provided the unsaturated pyridazinone derivative 32. A second route to pyridazine derivatives involves DDQ-mediated oxidation of dihydrofurans and reaction of the products with hydrazine hydrate. This leads to 4-methoxypyridazines 33, 34, 35, and 36 in good overall yields. The oxidative transformations of dihydrofuran derivatives reported here demonstrate new examples of reactivity umpolung; the lithiated alkoxyallenes are equivalents of the unusual synthons B and C, which represent anions of malondialdehyde or malonaldehydic acid.
