Acetate precursor route

Acetate Precursor Route. The use of acetate groups as elimination functionalities in a PPV precursor polymer have been reported. This precursor polymer is obtained from the sulfonium precursor... 

Later on, Ballard et al. [42, 43] developed an improved precursor route starting from 5,6-diacetoxycyclohexa-1,3-diene (18), the so-called 1C1 route. The soluble precursor polymer 19 is finally aromatized thermally into PPP 1 via elimination of two molecules of acetic acid per structural unit. Unfortunately, the polymerization of the monomer does not proceed as a uniform 1,4-polymerization in addition to the regular 1,4-linkages ca. 10% of 1,2-linkages are also formed as result of a 1,2-polymerization of the monomer. 

In 1992/1994, Grubbs et al. [29] and MacDiarmid et al. [30] described an improved precursor route to high molecular weight, structurally regular PPP 1, by transition metal-catalyzed polymerization, of the cyclohexa-1,3-diene derivative 14 to a stereoregular precursor polymer 16. The final step of the reaction sequence is the thermal, acid-catalyzed elimination of acetic acid, to convert 16 into PPP 1. They obtained unsupported PPP films of a definite structure, which were, however, badly contaminated with large amounts of polyphosphoric acid. 

Hybrid, chelate, or molecularly modified precursor routes also utilize alkoxide compounds for the B-site species. Unlike true sol-gel processes, these routes rely on molecular modification of alkoxide compounds through reactions with other reagents, namely chelating ligands, such as acetic acid, acetylacetone, or amine compounds. Despite this difference, chelate processes stiU share several common attributes with methoxyethanol-based sol-gel processes, most importantly, the formation of oligomeric species during solution synthesis. 

In addition to the use of heterometal alkoxides, metal alkoxides are often associated with more easily available precursors such as acetates for the SG route to multicomponent oxides. A number of such alkoxide acetate precursors [e.g., MNb2(/i-OAc)2(/i-OR)4(OR)6 (M = Cd or Mg), PbZr3(/t4-0)(/i-0Ac)2(/i-OR)5(OR)5, and Gd2Zr6(/i4-O)2(pi-OAc)6(/t-OR)l0(OR)i0 (with R = i-Pr)] were characterized (564) by X-ray crystallography. Their hydrolytic studies indicate their potential use as precursors for the synthesis of electrooptical materials, for example, Pb(ScNb)03 (PSN), and dielectric ceramics, for example, [PbMg1/3Nb2/303] (PNM). 

Poly(p-phenylene) (PPP) is a widely explored conjugated polymer in the field of PLED materials, Fig. 14 [67]. The presence of large band gap in the polymer reveals its blue emission characteristics. PPPs are insoluble and intractable in nature and therefore researchers have explored routes to synthesize soluble PPP films and a variety of PPP precursor routes have been discussed in literature [68]. PPP precursor routes involve the thermal elimination such as the elimination of two equivalents of acetic acid (per monomer unit) from poly-l,4-(5,6-diaceto-2,3-cyclohexene). This... 

A better product can be obtained if the precursor polymer contains some conjugated bonds which restrict the final structure and ensure extended conjugated-sequences. The most prominant example, is the Durham precursor-route to (equation 1). The precursor polymer is soluble in acetone, ethyl acetate, etc, and can be purified and cast to make films. The thermal elimination reaction produces cis-PA as the predominant form at 60 °C. Use of higher temperatures leads to higher proportions of trans-FA due to cis-trans isomerization. If the precursor film is unoriented the PA produced is amorphous. Stretching the precursor film during elimination leads to a highly oriented non-fibrous form of PA. trans-VA produced in this way exhibits a paracrystalline structure. 

Acetylation of acetaldehyde to ethyUdene diacetate [542-10-9], a precursor of vinyl acetate, has long been known (7), but the condensation of formaldehyde [50-00-0] and acetic acid vapors to furnish acryflc acid [97-10-7] is more recent (30). These reactions consume relatively more energy than other routes for manufacturing vinyl acetate or acryflc acid, and thus are not likely to be further developed. Vapor-phase methanol—methyl acetate oxidation using simultaneous condensation to yield methyl acrylate is still being developed (28). A vanadium—titania phosphate catalyst is employed in that process. 

The formation of an enamine from an a,a-disubstituted cyclopentanone and its reaction with methyl acrylate was used in a synthesis of clovene (JOS). In a synthetic route to aspidospermine, a cyclic enamine reacted with methyl acrylate to form an imonium salt, which regenerated a new cyclic enamine and allowed a subsequent internal enamine acylation reaction (309,310). The required cyclic enamine could not be obtained in this instance by base isomerization of the allylic amine precursor, but was obtained by mercuric acetate oxidation of its reduction product. Condensation of a dihydronaphthalene carboxylic ester with an enamine has also been reported (311). 

The wide applicability of the PK reaction is apparent in the synthesis of pyrroles, for example, 45, en route to novel chiral guanidine bases, levuglandin-derived pyrrole 46, lipoxygenase inhibitor precursors such as 47, pyrrole-containing zirconium complexesand iV-aminopyrroles 48 from 1,4-dicarbonyl compounds and hydrazine derivatives. The latter study also utilized Yb(OTf)3 and acetic acid as pyrrole-forming catalysts, in addition to pyridinium p-toluenesulfonate (PPTS). 

In a related study, the precursor 41 could be amiulated either by irradiation or by treatment with palladium acetate in acetic acid to provide indolocarbazoles 42 and 43 in yields of 37% and 55%, respectively (Scheme 8). Both products were eventually deprotected efficiently to give 44 and transformed further under reductive conditions to staurosporinone 45, the aglycone of 8, Alternatively, a shorter route encompassing deprotection of 41, followed by cychzation by irradiation in the presence of iodine and subsequent reduction, gave 45 in an even better overall yield (98T6909). 

Another route presented in the work cited above also finally furnished 16 and 17, although in this case, the intermediate 62, prepared in three steps from indigo (63) via the 0-acetates 64 and 65, served as the precursor leading to the key compound 61 (Scheme 10) [97H(45)1647]. Details of the synthesis of 64 had been given previously by Bergman (82CS193). 

The preparaticai of 2 from the carbazole derivative 112 provided yet another alternative route (Scheme 14). The precursor 113 was obtained from 112 by heating with phenylhydrazine in ethanol in the presence of acetic acid, followed by... 

Allyl acetate is a precursor for 1,4-butanediol via a hydrocarbonylation route, which produces 4-acetoxybutanal. The reaction proceeds with a Co(CO)g catalyst in benzene solution at approximately 125°C and 3,000 pounds per square inch. The typical mole H2/CO ratio is 2 1. The reaction is exothermic, and the reactor temperature may reach 180°C during the course of the reaction. Selectivity to 4-acetoxybutanal is approximately 65% at 100% allyl acetate conversion. ... 

Isoprene itself is not the true biological precursor of terpenoids. As we ll see in Chapter 27, nature instead uses two "isoprene equivalents"—isopentenvl diphosphate and dimethylallyl diphosphate—which are themselves made by two different routes depending on the organism. Lanosterol, in particular, is biosynthesized from acetic acid by a complex pathway that has been worked out in great detail. 

Terpenoid substances are of broad distribution and diverse function in insects. One set, elaborated by the mandibular glands of Acanthomyops claviger, acts both as a defensive secretion and as an alarm releaser. When fed Cu-labeled acetate or mevalonate, laboratory colonies of these ants produce radioactive citronellal and citral, providing unambiguous evidence for de novo synthesis of these terpenes by the ant. The incorporations of these precursors implicate the mevalonic acid pathway as the likely biosynthetic route. 

This section is completed with a brief review of the synthesis and properties of this epimer (20) of the precursor of thiazole in bacteria. This pentulose is conveniently accessible by an unconventional route (Scheme 19). Methyl 2,3 4,6-di-O-isopropylidene-a-D-mannopyranoside, readily available from methyl ot-D-mannopyranoside, is converted to the ketonic glycoside by butyllithium in 91% yield, following a method first published by Klemer and Rodemeyer43 and scaled up by Horton and Weckerle.44 This was converted by means of lithium hydroxide in a water-ether mixture into 3,5-0-benzylidene-l-deoxy-D-eryf/iro-2-pen-tulose in 55% yield. Hydrolysis to the free pentulose (20) proceeded in 73% yield in aqueous acetic acid. This product was obtained as a syrup with a characteristic absorption band at 1705 cm 1 as a film. Thus, there is a fair proportion of the open-chain ketone under these conditions, as with the D-threo epimer.45... 

The conversion of nitroalkanes to ketoximes can be achieved by the reduction with Zn in acetic acid,112 or Fe in acetic acid.113 Nitroalkenes are direcdy reduced into saturated ketoximes by these reagents, which are precursors for ketones (see Section 6.1.4 Nef reaction). Reduction of 3-O-ace-ty lated sugar 1 -nitro-1 -alkenes with Zn in acetic acid gives the corresponding 2,3-unsaturated sugar oximes in high yield, which is a versatile route to 2,3-unsaturated sugar derivatives (Eq. 6.58).114... 

Allyl acetals154). Allyl ethers give no or only trace amounts of ylide-derived products in the Rh2(OAc)4-catalyzed reaction with ethyl diazoacetate, thus paralleling the reactivity of allyl chloride. In contrast, cyclopropanation must give way to the ylide route when allyl acetals are the substrates and ethyl diazoacetate or dimethyl diazomalonate the carbenoid precursors. 

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