Mechanisms with furan

The highest mechanical strengths are usually obtained when the fibre is used in fine fabric form but for many purposes the fibres may be used in mat form, particularly glass fibre. The chemical properties of the laminates are largely determined by the nature of the polymer but capillary attraction along the fibre-resin interface can occur when some of these interfaces are exposed at a laminate surface. In such circumstances the resistance of both reinforcement and matrix must be considered when assessing the suitability of a laminate for use in chemical plant. Glass fibres are most commonly used for chemical plant, in conjunction with phenolic resins, and the latter with furane, epoxide and, sometimes, polyester resins. 

The formation of a diverse array of five-membered ring heterocycles via the cycloaddition of isocyanides with furan- or pyrrole-based enones was reported. The reaction mechanism is discussed and an example is shown below <06OL3975>. 

Reactions by Arenes In 2000, the first evidence of a gold-catalyzed hydroarylation of a, 3-unsaturated alkenes was reported by Hashmi et al. in their research with furans. In this publication, they proposed two possible mechanisms for the process ... 

The reaction of furans with ammonia and its derivatives is of considerable synthetic utility (B-73MI31 too). Substituted furan-2-carbaldehydes and 2-acylfurans on heating with ammonia and ammonium salts, often under pressure, yield 3-hydroxypyridines. The mechanism of this reaction is thought to involve nucleophilic attack of ammonia at the 2-position. Ring opening affords an amino aldehyde or ketone and thence, by reclosure, the 3-hydroxy-pyridine (Scheme 29). A wide range of substitutents is tolerated. Primary amines with furan-2-carbaldehydes yield A-substituted pyrroles, the closure of the intermediate... 

Density functional theory computational studies have been used to determine die importance of secondary orbital interactions for the stability of transition-state structures for die 4 + 2-cycloaddition of furan with cyclopropene.175 Kinetic studies of die 2 + 4-cycloaddition of 2-cyclopropylidene acetates with furan and dimethylful-vene suggest a mechanism involving diradicals or zwitterions as intermediates.176 Cyclopropene, produced by die reaction of allyl chloride with sodium bis(bimediyl-silyl)amide, reacts with 1,3-diphenylisobenzofuran to produce both endo- and exo-Diels-Alder cycloadducts isolated for the first tune.177... 

Perhaps more informative are the data in Table 22 for the relative rates of reaction of various cyclopropanones with furan. The results are consistent with the mechanism given in Scheme 32 where k >kz [furan], although the kinetic data do not distinguish between the closed cyclopropanone form and the zwitterionic intermediate. Increasing substitution would, of course, increase the stability of the allyl cation. 

Two examples are presented in which the intramolecular nucleophilic attack of adjacent alcohol groups led to the formation of spiro compounds (Schemes 11.12 and 11.13). In 2008, spirolactone 80 was synthesized in CH2C12 from an MB-sensitized photooxygenation of furan 79 [82]. A possible mechanism, with an... 

Tetrahalocyclopropenes also undergo the cycloaddition 232), and stereochemical studies, the effect of solvent and activation parameters appear to be consistent with a concerted mechanism 233). In these cases, endo-adducts are formed with furan. 3-Chloro-, 1,3-dichloro- and 3,3-difluorocyclopropenes add to cyclopentadiene to give endo-adducts 233,234). 

Dinitro-6-phenyliodonium phenolate (146) is a stable iodonium zwitterion484. It reacts under photolytic conditions with various alkenes, alkynes and aromatic compounds to afford 2,3-dihydrobenzo[ ]furans, benzo[6]furans and 6-aryl-2,4-dinitrophenols. The mechanism involves hypervalent iodine compounds (iodinanes, 147) and is illustrated for the reaction with an aromatic compound (equation 127). Compounds 148 are the major products when ArH = PhH, PhOCH3 or 1,4-dimethoxybenzene. With furan and thiophene, 149 is the principal product. The reaction does not proceed with chlorobenzene and nitrobenzene. 

In a previous section (Section 2.4.5), it was noted that the photoreaction of aldehydes containing an asymmetric center adjacent to the carbonyl with furan results in the production of a 1 1 ratio of two exo photoproducts. Irradiation of 2-phenylpropanal and furan results in a nearly quantitative yield of exo photoproducts (245) and (246) in approximately a 1 1 ratio. This suggests a mechanism that is insensitive to the substitution pattern of the aldehyde one such mechanism is depicted in Scheme 25. Reaction of an excited carbonyl and the electron-rich furan proceeds with initial carbon-oxygen bond formation to pro-... 

Couture showed that methyl- and dimethylthiophene on irradiation in a primary amine gave pyrroles and proposed a mechanism where the first step is the formation of a thioketone or a thioaldehyde by analogy with furan photochemistry (Scheme 2).7... 

CIDNP experiments have also been performed to gain insight into the mechanisms of PET induced [2 + 4] cyclizations of quinones with allenes [119], as well as of the photocyloadditions of chloranil with furan derivatives [120] and with N-vinylpyrrolin-2-one [121]. The sensitized valence isomerizations of norbomadiene and quadricyclane have received some... 

The kinetic stoicheiometry and mechanism of action of electrogenerated bromine with furan, pyrrole, and thiophen have been studied in detail/ Electrochemical trifluoromethylation of 2,5-dihydrothiophen 1,1-dioxide has been carried out/ ... 

Fluorinated diacylperoxides were also used as the source of fluoroalkyl radicals. The electron-transfer mechanism was proposed for the reaction of compound 21 with furan. ... 

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