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

Abstract

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 b-alkoxy butenolides by a manganese(III) acetate catalyzed radical oxidation with tert-butyl hydroperoxide, or transformed into a,b-unsaturated g-keto aldehydes by an oxidative ring cleavage using DDQ in the presence of water. Treatment of the g-keto aldehydes with sodium methoxide in methanol promotes a diastereoselective intramolecular aldol addition furnishing alkoxy-substituted cyclopentenone derivatives in good yield.

Hetero‐Diels‐Alder‐Reaktionen von Nitrosocarbonylverbindungen als nützliches Verfahren in der organischen Synthese

“…[4,10,17] Cyannitroso-(4), [17] Arylnitroso-(9), Pyridylnitroso- (10), [18] a-Halogennitroso-(5), [19][20][21] a-Acetoxynitroso- (6), [22,23] Vinylnitroso-(7), Iminonitroso-(8) [24] und Acylnitroso-Verbindungen 11 [17] sowie Nitrosoformiate 12 [25] sind gängige Beispiele für in HDA-Transformationen verwendete Verbindungen.…”

“…[17] ¾hnliche Effekte wurden für in a-Position substituierte Nitrosoalkane beobachtet, zum Beispiel für die Chlornitrosospezies 5 [19][20][21] und die Acetoxynitrosospezies 6. [22,23] Bei den reaktivsten Nitrosoverbindungen handelt es sich um direkt mit elektronenziehenden Gruppen verknüpfte, weswegen 4, 8, 11 und 12 unter den reaktivsten in HDA-Reaktionen verwendeten Nitrosodienophilen sind.…”

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C3-building block

“…During our current studies on the synthesis of highly functionalized heterocycles utilizing alkoxyallenes as versatile C 3 -building blocks we chose jaspine B ( 1 ) as an attractive target [29–33]. Our approach to 1 is based on the addition of a lithiated alkoxyallene with a chiral auxiliary to pentadecanal as electrophile.…”