Furan 2-carboxaldehyde

El Haji, T. Masroua, A. Martin, J.-C. Descotes, G. Synthesis of 5-(hydroxymethyl)-furan-2-carboxaldehyde and its derivatives by acid treatment of sugars on ion-exchange resins, Bull Soc. Chim. Fr., 1987, 855-860. 

Dielectric absorption on furan-2-carboxaldehyde has been measured (78JCS(F2)727 81ZPC147). Even in a polymer matrix, the energy barrier obtained for internal rotation is close to that determined with other experimental techniques, suggesting a low influence of the surrounding medium on the torsional process. 

As examples of the conformational behavior of these derivatives, a number of selected experimental results have been gathered in Table I Those referring to furan-2-carboxaldehyde show the wide range of conformational composition found in different solvents. 

Thus, aside from furan-2-carboxaldehyde, where the equilibrium between conformers is rather sensitive to external effects, the 2-formyl derivatives of five-membered heterocycles are rather rigid from a conformational point of view. 

In mobile equilibria, the increase in the dielectric constant of the solution should enhance the population of the conformer with higher polarity (SOM 18), as is also proved by theoretical calculations. The solvation energy may lead to inversion in isomer stability on going from the vapor phase to a solution of a certain polarity, as occurs for furan-2-carboxaldehyde (72T3015). Inversion in conformer stability may also occur on going from the vapor to the liquid or solid state. 

Conversely, furans with electron-withdrawing groups e.g. CHO, CN, C02Me) in the 2-position show reduced Diels-Alder reactivity. Although furan-2-carboxaldehyde is a poor diene the related N,N-dimethylhydrazones do take part in reactions with a range of dienophiles including maleic anhydride, maleimides, and fumaronitrile (88JOC1199). 

Heterocyclic and aromatic aldehydes (e.g., furan-2-carboxaldehyde, thiophen-2-carboxaldehyde, the pyridine carboxaldehydes, benzaldehyde, and diverse substituted benzaldehydes). 

The first example of a tandem Ugi-4CR/intramolecular Diels-Alder reaction was reported by Paulvannan at Affimax [95], who obtained precursors for intramolecular Diels-Alder cycloadditions by an Ugi-4CR between furan-2-carboxaldehydes, monoamides or monoesters of fumaric or maleic acids, benzylamine, and benzyl isocyanide. The Ugi-4CR adducts 172 were never isolated since they underwent... 

T. Hofmann, Characterization of chemical structure of novel colored Maillard reaction products from furan-2-carboxaldehyde and amino acids, J. Agric. Food Chem., 1998, 46, 932-940. 

T. Hofmann, Studies on melanoidin-type colourants generated from the Maillard reaction of casein and furan-2-carboxaldehyde — chemical characterisation of a red coloured domaine, Z. Lebensm. Unters. Forsch, 1998, 206, 251-258. 

A novel one-pot three component synthesis of l,2,4-triazino[3,4-6]thiazolones 60 has been described by condensation of mercaptotriazinones 58, 5-aryl-furan-2-carboxaldehyde 59 and chloroacetic acid <05SC333>. 

Furans are volatile, fairly stable compounds with pleasant odours. Furan itself is slightly soluble in water. It is readily available, and its commercial importance is mainly due to its role as the precursor of the very widely used solvent tetrahydrofuran (THF). Furan is produced by the gas-phase decarbonylation of furfural (2-formylfuran, furan-2-carboxaldehyde), which in turn is prepared in very large quantities by the action of acids on vegetable residues mainly from the manufacture of porridge oats and cornflakes. Furfural was first prepared in this way as far back as 1831 and its name is derived from furfur which is the latin word for bran in due course, in 1870, the word furan was coined from the same root. 

The temporary protection of furancarboxaldehydes as a device to direct metallation has been used in a number of different ways. Lithiation of the diethylacetal of furan-2-carboxaldehyde occurs... 

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