Synthesis alkynyl Furan

Wipf and co-workers developed a base-catalyzed cyclization of alkynyl ketones into a general synthesis of furans. The authors then extended the... 

Alternative Strategies for Synthesis of Compounds 130 to 133 Based on C-Alkynyl Furan Derivatives... 

Recently, a highly selective gold-catalyzed synthesis of anelated phenol derivatives (e.g., 31) from 8-alkynyl furans (e.g., 30) was developed [14] ... 

D. Conreaux, S. Belot, P. Desbordes, N. Monteiro, G. Balme, EtsN-induced demethylation-annulation of 3-alkynyl-4-methoxy-2-pyridones and structurally related compounds in the synthesis of furan-fused heterocycles, J. Org. Chem. 73 (2008) 8619-8622. 

The add-catalyzed cyclodehydration of (Z)- and ( )-6-hydroxy-a,p-unsaturared ketones offers a mild synthesis of substituted furans. In the case of ( )-olefins, photochemical isomerisation was found to accelerate the reaction <96TL6065>. Reaction of alkynyl(phenyl)iodonium tetrafluoroborates with tropolone in the presence of a base yields 2-substituted furotropones (Scheme 16, <96TL5539>). 

A related synthesis of highly substituted furans was reported by Schmalz and Zhang from cyclopropyl alkynyl ketones. The reaction scope included a great variety of nucleophiles such as several alcohols, indole or even acetic acid [140]. 

A synthesis of [3]-fused furans involving a ring enlargement can be effected by the treatment of a-alkynyl-a-cyclopropylcycloalkanones with an electron-rich Au(l) catalyst in the presence of a suitable nucleophile (Equation 18) <2006AGE6704>. The nucleophiles that can be used include alcohols, phenols, carboxylic acids, indole, and 2-pyrrolidone. Open-chain ketones as well as other ring sizes react with comparable yields. Silver and lanthanide triflates are also effective catalysts for this transformation. 

A concise synthesis of highly substituted furans, pyrroles, butenolides, and 2-butene-4-lactam esters starts from alkynyl adducts of a Fischer carbene complex 21 (Scheme 27) < 1998JOC3164>. Incorporation of an aldehyde yields a reactive vinyl tungstencarbonyl complex 22 that can be oxidatively transformed to an ester group, furnishing the furan carboxylic ester 23. 

Metalatlon of 2-alkynyl and 1,2-alkadienyl tetrahydropyranyl ethers furane synthesis. /-Butyllithium metalates the lithium alkoxide 1 to afford the allenyllithium compound a quantitatively. This anion reacts with alkyl halides or CH3OH to afford 2. Another metalation-alkylation protonation sequence proceeds via b to afford 3. Hydrolysis of the latter intermediate affords furanes directly. The overall sequence can be performed in one pot from a propargyl tetrahydropyranyl ether, r-butyl-lithium, and an aldehyde. ... 

An efficient and atom-economical Au-catalyzed poly substituted furan synthesis was reported <04JA11164>. As can be seen, Au-catalyzed cyclization of 2-(l-alkynyl)-2-alken-l-ones in the presence of MeOH as a nucleophile afforded 2,3,5-trisubstituted furans with high regioselectivity and high yields. A variety of alcohols, 1,3-diketones, some indoles, and amines can serve as nucleophiles. 

Heterocycles. Alkenyl and aryl boronates deliver their organic residues to the opposition of the nitrogen atom of cyclic carbinolamines to replace the hydroxyl group. Synthesis of 2,3,5-trisubstituted furans, from a catalyzed reaction of alkynyl borates and enones, is achieved in one step. 

Recently, a novel approach for the synthesis of highly substituted furans vas developed by Larock and covrorkers (Scheme 8.37). It vas reported that 2-alkynyle-nones [151-153] 93 undervrent a facile transition metal-catalyzed cycloisomerization affording highly substituted furans 94 in the presence of the external O- or electron... 

Scheme 3.24 Cu-catalyzed decarboxylative coupling of alkynyl carboxylic acids (a) and decarboxylative furan synthesis (b), as described by Xue and coworkers [41].

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