Multi-furan

Re-mendable polymers can achieve multiple healing cycles, but require external intervention in the form of heat treatment and applied pressure. It is a powerfiil method of crack reparation for polymers that exhibit thermally reversible reactions for cross-linking linear chains. For example, a Diels-Alder polymerization product of reaction between a multi-furan and multi-maleimide has shown to be feasible and a recovery of about 57% of the original fracture load has been obtained. Other types of organic adhesives are not capable of repolymerizing, and alternative self-healing procedures should be employed. 

As can be seen in the scheme below, the catalytic activity of gold species was also shown in a multi-substituted furan synthesis. Cyclization of allenones in the presence of Au(III)-porphyrin gave rise to the corresponding substituted furan in good to high yields. The catalyst can be recycled several times and still maintain the same catalytic activity <06OL325>. 

Substituted furan formation by an indirect cyclization of 1,4-dicarbonyl derivatives has also been adopted as a key step in the synthesis of 3-oxa-guaianolides. Although 1,4-dicarbonyl compounds have been traditionally considered as the direct precursors for furans, treatment of 1,4-dicarbonyl compounds having a tertiary acetoxy group with p-toluenesulfonic acid leads to only 11% yield of an alkenylfurans as derived from a cyclization/acetoxy-elimination route. The following scheme shows an alternative multi-step conversion of the 1,4-dicarbonyl that leads to a more acceptable yield of the acetoxyfuran . 

Arimitsu, S. Jacobsen, J. M. Hammond, G. B. Synthesis of Multi Substituted 3-Fluoro Furans and 3,3-Difluoro Hydrofurans. Proceedings of the 233rd American Chemical Society National Meeting, Chicago, IL, March 25-29, 2007. 

Benzoheteropines with fused pyrrole, furan, and thiophene rings, of great interest because of their biological activity, are surveyed by Dr. D.O. Tymoshenko of the Albany Molecular Research Institute, New York. These compound classes were considered in both the first and second editions of Comprehensive Heterocyclic Chemistry as part of a host of related multi-atom heterocyclic systems. Other specialized reviews have appeared. However, the present survey is the first comprehensive treatment. 

The CIR is exceptionally well suited as an entry to multi-component syntheses of aromatic heterocycles and on this basis Muller and coworkers [91f, 92] designed a coupling-isomerization-Stetter-Paal-Knorr sequence as a diversity-oriented approach to highly substituted furans and pyrroles (Scheme 5.22). 

Since all novel furans 95 and pyrroles 98 exhibit a strong blue fluorescence with considerable Stokes shifts, where the absorption maxima are found in the range 7.max, abs = 312-327 nm and the emission occurs at 7,max at,s = 401-451 nm, this multi-component approach to fluorophores can be exploited for combinatorial optimization of emission properties. 

Tsukube 14) reported in 1984 a multi-armed cyclam (18) which has the ability to transport NH4+ cation through a chloroform layer (a so-called liquid membrane ). Metal ions such as K+ are not transported under similar conditions, a selectivity generally unobserved with the common crown ethers and cryptates. Since the transport rate decreases substantially when the furan rings terminating the pendant arms are... 

Several protocols using multi-component reactions to prepare multisubstituted furans were reported. One procedure was that using acetylenedicarboxylate, isocyanides, triphenylphosphine and an aromatic carboxylic acid <07SL1610>. The others include the reaction of acetylenedicarboxylate, isocyanides and nicotinic acid <07S2637>, of dibenzoylacetylene, amines and diketene <07T8083>, of alkyl isocyanides, aromatic aldehydes and 3-cyanoacetyl indoles <07TL8987>, and of naphthoquinone, isocyanides and aldehydes <07T10269>. 

A multi-gram enantioselective synthesis of (+)-37, a key precursor to the tetracycline antibiotics, has been performed from simple heterocyclic compounds. Key steps in the route involve enantioselective addition of divinylzinc to 3-benzyloxy-5-isoxazolecarboxaldehyde (with 93% ee) for the preparation of 36 and, after its nucleophilic addition to 35, an intramolecular furan Diels-Alder cycloaddition <07OL3523>. 

Multi-ring heteroaromatic compounds containing furan and thiophene rings have been prepared by pressured cycloaddition of 2-vinylbenzo[ ]furan (40a) and 2-vinylbenzo[Z)]thiophene (40b) with 3-nitro-2-cyclohexen-l-one (41) and 2-inden-l-one (42), respectively, generated in situ. ... 

Furfural and thence furan, by vapour-phase decarbonylation, are available in bulk and represent the starting points for many furan syntheses. The aldehyde is manufactured from xylose, obtained in turn from pentosans, which are polysaccharides extracted from many plants, e.g. com cobs and rice husks. Acid catalyses the overall loss of three mole equivalents of water in very good yield. The precise order of events in the multi-step process is not known for certain, however a reasonable sequence " is shown below. 

There has probably been more work carried out on the synthesis of indoles than on any other single heterocyclic system and consequently many routes are available ring syntheses of benzo[Z ]furans and benzo[fc]thiophenes have been much less studied. The Fischer indole synthesis, now more than 100 years old, is still widely used - an arylhydrazone is heated with an acid, a multi-step sequence ensues, ammonia is lost and an indole is formed. 

Beside this, the products used in the practice are often mixtures of several substances with different partition coefficients, that is why single representatives fall into different categories. For instance the lighter Dioxins and Furans are in category B (multi hop), but the heavy Dioxins and Furans get into category C ( single hop ). 

The SAC-CI general-R method is useful for investigating the satellite spectrum of molecules it describes the multi-electron process very accurately. The SAC-CI spectrum [54] of furan is shown with the SRPES spectrum [64] in Fig. 39.3. The SAC-CI method reproduces the spectrum very accurately in both peak positions and intensities. In the outer-valence region, some congested main peaks exist and the theory gives accurate assignments for them. In particular, the tti state was calculated to split into two peaks at... 

Several quinonoid azuleno[c]furans can be prepared by a tandem cycloaddition-cycloreversion strategy in the course of multi-step syntheses (Scheme 34), the furan ring being introduced at an early stage (03OBC2383). Thus, the cycloaddition of sulfone 144 (generated in situ)... 

A palladium(ll) catalyst promoted condensation of an Al-aryl imine and an alkynylbenzodioxolone derivative to afford a multi-substituted furan, with substituents derived from the alkynyl moiety (2-position), the imine (3- and 4-positions), and the 2-iodobenzoate moiety (5-position), along with an N-arylformamide under mild conditions (14JA11598). 

Practical and diversity-oriented synthesis of multi-substituted benzo[lr] furans was accomplished from simple phenols through a Pummerer annula-tion/cross-coupling sequence. Operationally simple and rapid reactions of phenols with ketene dithioacetal monoxides with the aid of trifluoroacetic anhydride provided the corresponding 2-methylsulfanylbenzo[ ]furans (14BCJ1349). 

Subsequently, Donohoe and co-workers also reported the RCM reaction of MBH derivatives 243, and the crude RCM products were further transformed, via elimination of methanol, into the fully aromatized system (a reaction promoted by adding acid). As shown in Scheme 4.78, multi-substituted furans 244 have been prepared in 59-81% yields in a one-pot process. ... 

The extension of these DA-hased polymerizations to multi-functional furan and/or maleimide monomers naturally leads to crosslinked materials, whose original feature is related to the fact that they can be readily decrosslinked by a simple thermal treatment. Since the first report of a mendable material based on this principle, but applied in cycles [69], several similar studies have appeared in the literature [64] including interesting applications in the realm of thermally removable foams [64] and adhesives [64]. It seems likely that such a simple and useful strategy will continue to draw attention for the preparation of novel intelligent materials. 

Chaplin, J.H. and n3mn, B.L. (2001) A multi-component coupling approach to benzo[(>]furans and indoles. Chem. Commun., 1594—5. 

Multi-armed cyclam" bearine furan oxygen atoms on its four arms mediated specific transport of NH cation across a liquid membrane, while H, K, and other metal cations were hardly transported under the employed conditions. Since simple cyclam derivatives fi and exhibited low transport rates of NH cation, the furan oxygen atoms attached to the cyclam ring may play an important role in complexation and transportation of NH cation. ... 

Dimethoxy-2,5-dihydrofurfuryl alocohl dissolved in 2%-H2S04, and allowed to stand 1.5 hrs. at room temp. 2,3-dideoxy-DL-pent-2-enopyranos-4-ulose. Y ca. 100%. - This is a stage of a multi-step conversion of furan derivs. into monosaccharides. F. e. s. O. Achmatowicz, Jr., et al.. Tetrahedron 27, 1973 (1971) 6-hydroxy-2,6-dihydro-3-pyrones from furylcarbinols by oxidative ring expansion cf. Y. Lefebvre, Tetrah. Let. 1972, 133. 

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