Furan derivatives, alternative

On the other hand, we also planned alternative completely new approach (Route B) to Nakadomarin A, which involves the spirolactam followed by coupling reaction with furan derivative and subsequent intramolecular electrophilic substitution reaction of an iminium cation generated from an aminal to give highly functionalized tetracyclic core system (Scheme 10.3). 

Preparation of addition polymers having the oxolene (dihydrofuran) functionality can be envisioned to occur in two possible ways (Scheme 13). Both, in fact, have been observed (77MI11102). Whereas furan (53) or its derivatives do not homopolymerize under free radical conditions, 1 1 alternating copolymers possessing the 1,4-structure are produced with maleic anhydride (50). Intermediate formation of a CT complex between monomers (50) and (53) is believed to be necessary before polymerization can occur. On the other hand, cationic polymerization is quite facile. The outcome is straightforward with benzo[f>]furan derivatives, producing 1,2-polymers. Optically active poly(benzofurans) are formed when the cationic polymerizations are conducted in the presence of a chiral anion. 

Preliminary investigations demonstrate that [19] is an excellent reactant for forming heterocycles. Hvdrolysis of [19] occurs quantitatively, to give the known (15) furan derivative [24]. Indeed, it is difficult to avoid forming some of the furan unless solvents are kept scrupulously dry. Obviously, for the cyclisation to proceed, then there must be interconversion of isomers and we can think of alternate processes for forming [24], as shown. 

In the above condensation resist designs, the phenolic resin offers a reaction site as well as base solubility. Self-condensation of polymeric furan derivatives has been utilized as an alternative crosslinking mechanism for aqueous base development (Fig. 126) [375]. The copolymer resist is based on poly[4-hydroxy-styrene-co-4-(3-furyl-3-hydroxypropyl)styrene], which was prepared by radical copolymerization of the acetyl-protected furan monomer with BOCST followed by base hydrolysis. The furan methanol residue, highly reactive toward electrophiles due to a mesomeric electron release from oxygen that facilitates the attack on the ring carbons, readily yields a stable carbocation upon acid treatment. Thus, the pendant furfuryl groups serve as both the latent electrophile and the nucleophile. Model reactions indicated that the furfuryl carbocation reacts more preferentially with the furan nucleus than the phenolic functionality. 

Alternative Strategies for Synthesis of Compounds 130 to 133 Based on C-Alkynyl Furan Derivatives... 

Two striking differences distinguish the essence of this chapter from most other chapters, namely (i) the fact that the furan compounds relevant to polymer synthesis are not found as such in nature but are instead obtained from parent renewable resources and (ii) it is possible in principle to envisage a whole new realm of polymer materials based on furan monomers and furan chemistry, covering a very wide spectrum of macromolecular structures. Concerning the first point, the massive availability of saccharidic precursors and their relatively sirt5)le conversion into furan derivatives, eliminate in fact any apparent problem of absence of such natural structures. As for the second point, its unique relevance has to do with the potential perspective of a viable alternative to the present reality based on polymer chemistry derived from fossil resources. In other words, the biomass refinery concept would be applied here to the synthesis of different furan monomers, simulating the equivalent petroleum counterpart. 

Alternatively, 5-allyl-2(5/f)-furanones can be obtained from TMSOF and allylic acetates using lithium perchlorate in ether. 5-Propargyl-2(5//)-furanones are prepared by coupling with bex-acarbonyldicobalt complexes of propargylium cations (eq 5). Reaction of the intermediate complex with cerium(TV) ammonium nitrate removes the cobalt Fluoroalkylation is acbieved by using bis(fluoroalkanoyl) peroxides in 1,1,2-tricbloro-1,2,2-trifluoroethane (Freon 113) (eq 6). This process is believed to involve combination of a fluoroalkyl radical with the furan-derived radical cation. 

For decades, it has been well known that triafulvene reacts with various 1,3-dipoles, and the modes of the reaction depend on the nature of the 1,3-dipole as well as the substituents on the triafulvenes. For example, triafulvene 308 treated with pyridium ylide 309 to give pyran derivative 310 was reported by Eicher et al. The same reaction with methyl (triphenylphosphoranylidene)acetate 311 gave the cyclobutene derivative 312 (Scheme 7.68) [79]. Alternatively, treatment oftriaful-vene 308 with isoquinolinium ylide 313 afforded furan derivative 314. The mechanism of these reactions, proposed by the authors, is depicted in Scheme 7.69. 

Chemical dehydration is employed to syntiiesize HMF using six member carbohydrates. HMF can be converted into a variety of furan derivatives through chemical manipulation (Tong et al., 2010). 2,5-furandicarboxylic acid (FDCA) can be derived from the oxidation of ITMF. In the production of polyester polymers, FDCA is recommended as an alternative to terephthalic... 

An alternative route to 5-nitro-2-furancarboxaldehyde requires nitration of 2-furancarboxaldehyde oxime [1121 -47-7] with mixed acid to give the nitrated oxime [555-15-7] and concomitant hydrolysis (22). Furthermore, 2-furan-carboxaldehyde derivatives with the R-substituent in place have been nitrated to the desired product (23). 

The effect of substituents on the reactivity of heterocyclic nuclei is broadly similar to that on benzene. Thus mem-directing groups such as methoxycarbonyl and nitro are deactivating. The effects of strongly activating groups such as amino and hydroxy are difficult to assess since simple amino compounds are unstable and hydroxy compounds exist in an alternative tautomeric form. Comparison of the rates of formylation and trifiuoroacetylation of the parent heterocycle and its 2-methyl derivative indicate the following order of sensitivity to substituent effects furan > tellurophene > selenophene = thiophene... 

In many cases, substituents linked to a pyrrole, furan or thiophene ring show similar reactivity to those linked to a benzenoid nucleus. This generalization is not true for amino or hydroxyl groups. Hydroxy compounds exist largely, or entirely, in an alternative nonaromatic tautomeric form. Derivatives of this type show little resemblance in their reactions to anilines or phenols. Thienyl- and especially pyrryl- and furyl-methyl halides show enhanced reactivity compared with benzyl halides because the halogen is made more labile by electron release of the type shown below. Hydroxymethyl and aminomethyl groups on heteroaromatic nuclei are activated to nucleophilic attack by a similar effect. 

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 . 

Hydroxy derivatives of thiophene, pyrrole and furan (240 and 243) are tautomeric with alternative non-aromatic carbonyl forms (241, 242 and 244), as discussed in Section 2.3.5.2. 

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