Heterocyclic alcohols furfuryl alcohol

The reaction of the a-bromo aldoxime 52e (R = R = Me) with unsaturated alcohols has been extended to the heterocyclic systems furfuryl alcohols and 2-thiophene methanol [29b]. The furanyl and thiophenyl oximes 63a-c were treated with NaOCl and the resulting heterocyclic nitrile oxides were found to undergo spontaneous intramolecular dipolar cycloaddition to produce the unsaturated tricyclic isoxazolines 64a-c in high yield (Eq. 5). In these cases, the heterocyclic ring acts as the dipolarophile with one of the double bonds adding to the nitrile oxide [30]. 

Furfural (1), derived from annually renewable agricultural byproducts, is an important industrial chemical manufactured and used throughout the world. It is the feedstock for a number of derivative chemicals generically known as furans -the structural characteristic of which is the five-membered oxygen-containing heterocyclic ring. Furfuryl alcohol (2) is the most important derivative of commerce, where it is used primarily in synthesis of adhesive polymers. 

The distribution of oxygen heterocyclic compounds differs in Robusta and Arabica roasted coffees some concentration values are given in Table 9.39 Roasted Robusta contains relatively high proportions of furfuryl alcohol and the caramel flavored maltol (Figure 7) in comparison with roasted Arabica.39... 

Hydroxylic groups in positions a to heterocyclic aromatics undergo hydro-genolysis in catalytic hydrogenation. In the case of furfuryl alcohol, hydrogenation also reduces the aromatic nucleus and easily cleaves the furan ring giving, in addition to a-methylfuran and tetrahydrofurfuryl alcohol, a mixture of pentanediols and pentanols [38,420]. 

The diversity of polymers containing heterocyclic groups is quite large. These polymers may include macromolecules generated from the polymerization of a unique monomer, such as poly(furfuryl alcohol), CAS 25212-86-6, with the formula shown below ... 

Some polymers containing heterocycles can be included in resins following further condensation. This is possible, for example, for poly(furfuryl alcohol), which can condense with formaldehyde, phenol, melamine and urea. Furfuryl alcohol-formaldehyde copolymer can be synthesized in the reaction of furfuryl alcohol with formaldehyde in the presence of oxalic acid as catalyst. 

Depending on their structure, the polymers containing heterocycles have various applications. For example, poly(furfuryl alcohol) is used in composite materials with fillers such as sand and concrete, in copolymers with formaldehyde, etc. Some of the polymers from this group have special properties such as good electrical conductivity (after appropriate doping). Among these polymers are poly(thiophene-2,5-diyl) and particularly polypyrrole, CAS 109-97-7, (usually in carbon black doped with an organic acid anion). The structure of this polymer is shown below ... 

Fig. 5. Hydrogenation of the ring of heterocyclic compounds using 1 g. of 5% Rh on AI2O3 powder as catalyst and 100 ml. solvent. 1) 1 ml. pyridine, H2O 2) 1 ml. pyrrole, HOAc 3) 1 ml. 2, 5-dimethyl-furane, HOAc 4) 1 g. furoic acid, H2O 5) 1 ml. furfuryl alcohol, H2O.

The most common oxygen-containing heterocyclic alcohol is furfuryl alcohol, which is a degradation product of sugars. Furfuryl alcohol results primarily from furan-2-carbaldehyde by reduction or a Cannizzaro reaction. A large number of other alcohols derived from furan, pyran and other heterocyclic compounds are products of the Maillard reaction. 

A series of tetradentate pyridyl-imine terminated Schiff-bases, bis(pyridyl-imine) terminated siloxane and other related polymers, can be used as ligands to host copper(II) ions. These CuBr2/polyL/TEMPO catalytic systems (polyL stands for polydimethylsiloxane derived pyridyl-imine terminated ligand) are effective for aerobic oxidations of primary and secondary alcohols under aqueous conditions. Chiral N,0-Hgands, e.g., inexpensive L-proline, can also be used to prepare copper catalysts that are particularly effective for the oxidation of sterically hindered, allylic or heterocyclic alcohols such as l-(3-pyridyl)ethanol, l-(2-furfuryl)ethanol. 

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