Some Furan Derivatives

H-NMR for (t-Adduct Formation from Some Furan Derivatives (Reaction with MeO )... 

Application of electronic spectroscopy to conformational analysis of some furan derivatives has been reported. 

J.M. Garcia De La Vega, J. San Fabian, R. Crespo-Otero, R. Suardiaz, C. Perez, Conformational and NMR study of some furan derivatives by DFT methods, Int. J. Quant. Chem. 113 (2013) 656-660. 

A specific type of rancidity, known as reversion in the United States, occurs during the oxidation of soybean oil. Reversion is caused by some furan derivatives, such as 2-pentylfuran or (Z)- and ( )-2-(pent-2-en-l-yl)furan and other decomposition products of hydroperoxides. Pentylfuran arises (Figure 3.48) as a by-product of the decomposition of 9-hydroperoxyoctadeca-10,12-dienoic acid derived from linoleic acid via the terminal radical. The content of linoleic acid in soybean oil is about 51% of the total fatty acids. Similarly, both isomers (cis and trans) of 2-(pent-2-en-l-yl) furan (3-139) arise by decomposition of 9-hydroperoxyoctadeca-10,12,15-trienoic acid formed by autoxidation of linolenic acid. 

Cabanas, B., F. Villanueva, P. Martin, M.T. Baeza, S. Salgado, and E. Martinez (2005), Study of reaction processes of furan and some furan derivatives initiated by Cl atoms, Atmos. Environ., 39, 1935-1944. 

FtG. 2. Relative energy of the excited states of 2-methylfuraii and of some reactive intermediates. [Reprinted with permission from M. D Auria. Ab initio study on the photochemical isomerization of furan derivatives. J. Org. Chem. 65, 2494-2498 (2000)]. 

Some of the typical conditions of polycondensations used for aliphatic and aromatic monomers are not suitable for furan derivatives, e.g., the melt polycondensation of 2,5-furan dicarboxylic acid chloride with 2,5-b/s(hydroxymethyl) furan at about 80 °C only yields a black insoluble product5. The hydrochloric acid liberated in the reaction is clearly responsible for the charring of the furanic diol which like its simpler homologue furfuryl alcohol, resinifies rapidly in acidic media (see below). 

If on the other hand the polymerization of a furan derivative takes place through a substituent containing an adequate functionality, such as C=C or C=0, the furan ring should in principle conserve its structure and the polymers obtained will bear it as a side group. It has been found, however, that in some of these systems the normal propagation is accompanied by other reactions which involve participation of the ring and which therefore alter the normal structure of the macromolecule. The second section of this chapter deals with monomers, such as 2-vinylfuran and 2-furaldehyde, which exhibit this general behaviour. 

In this section some systems are briefly described which make use of furan derivatives as starting materials for chemical transformations which eventually lead to polymeric products. However, with the exception of Section (c), these final products bear little resemblance to the original furan compounds used and are, therefore, only marginally relevant to the context of the present review. 

Although the pyrolysis of some classes of polysaccharide materials has been studied quite extensively in the food, petrol and tobacco industry, very little has been published specifically on polysaccharide binders (arabic gum, tragacanth gum, fruit tree gum, honey and starch). The pyrolysis of glucane based polymers, especially cellulose, has been studied in detail [6,55], highlighting how anhydrosugars and furan derivatives are the main pyrolysis products, together with one-, two- and three-carbon aldehydes and acids. 

The acid XXVI was subsequently studied by Garcia Gonz lez.6 He was at first unable to isolate the furan derivative (III) after oxidation with 30 % hydrogen peroxide under the same mild conditions as had been used for converting compound II to this substance. Subsequently, the isolation of some 20% of compound III was successfully accomplished by oxidizing compound XXVI very slowly with potassium permanganate at low tempera-... 

In contrast to the rich chemistry of alkoxy- and aryloxyallenes, synthetic applications of nitrogen-substituted allenes are much less developed. Lithiation at the C-l position followed by addition of electrophiles can also be applied to nitrogen-containing allenes [10]. Some representative examples with dimethyl sulfide and carbonyl compounds are depicted in Scheme 8.73 [147, 157]. a-Hydroxy-substituted (benzotriazo-le) allenes 272 are accessible in a one-pot procedure described by Katritzky and Verin, who generated allenyl anion 271 and trapped it with carbonyl compounds to furnish products 272 [147]. The subsequent cyclization of 272 leading to dihydro-furan derivative 273 was achieved under similar conditions to those already mentioned for oxygen-substituted allenes. 

Furan Derivatives Catalytic processes used to obtain furan derivatives from carbohydrates and the catalytic routes from furan intermediates to chemicals and polymers have been reviewed by Moreau et al. [27]. Some of the main reactions are summarized in Fig. 3.2. From fructose or carbohydrates based on fructose (sucrose, inulin), the first transformation step is dehydration to 5-hydroxy methylfur-fural (HMF). Fructose dehydration at 165 °C was performed in the presence of... 

Other examples of the iodonium ylide-based syntheses of furan derivatives involve cycloaddition reactions with alkenes or alkynes. Although the majority of these syntheses involve stable iodonium ylides (86JOC3453 94T11541) (e.g., Eqs. 16 and 17), in some cases the ylides are unstable and are generated in situ (92JOC2135) (e.g., Eq. 18). In the case of alkenes, dihydrofuran derivatives are obtained (Eqs. 16-18). This synthetic route is especially useful for the synthesis of dihydrobenzofuran derivatives that are related to the neolignan family of natural products (Eq. 18). 

Rate and Equilibrium Constants for the Formation of ct-Adducts by the Reaction of Some Furan and Pyrrole Derivatives with MeO" at 25°C... 

Pd/C in AcOH515 539 or on Pd/BaS04 in AcOH,534 the reaction proceeds through to the 2,3-dihydrobenzofuran stage. Some catalysts (Raney nickel at 60° 50 kg/cm2) lead directly from 237 to 2,3-dihydrobenzo-furan derivatives, without going through the acetoxy derivatives.516 The corresponding benzofuran derivative is obtained under normal pressure.516... 

Most forms of the furan ring are common, however in the Cambridge file of structures determined by X-ray diffraction there are (at the time of writing) 28 978 entries of which 1829 are furan derivatives of one kind or another. Radicals involving furan nuclei have attracted some attention but are not discussed here except to mention two leading references <80AHCt27)31, 82AHC(30)167>. 

Many furan derivatives have been examined by X-ray diffraction methods, and natural products (especially the terpenoids) have provided numerous, interesting subjects for study. Some work has also been done by electron diffraction methods and, more recently, by microwave spectrometry. The bond lengths and angles determined for furan and assembled... 

The photochemistry of heterocyclic compounds was the object of a book published in 1976 and edited by Buchardt (76MI1). Here, the photochemistry of thiophene covers eight pages written by Lablache-Combier (76MI123). Some reviews have appeared since on the photochemical behavior of pyrrole and furan derivatives (89G419 96H(43)1305 96H(43) 1529) but apparently none on thiophene photochemistry. 

Among the important processes taking place when sucrose is heated is cara-melization. Caramel is actually a very complex mixture. Some constituents are volatile, such as furan derivatives, pyrones, aldehydes, and low molecular weight carboxylic acids, and these account for 10% of the mass.340 The main constituents of the nonvolatile component have also been identified these include... 

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