Propiolic anhydride

This isomerization is accompanied by a drop in conductivity. The polymer is also unstable in air, oxidising more rapidly than does Shirakawa polyacetylene. Both of these problems result from the allylic hydrogen atoms in the 3,5-positions of the monomer. In an effort to remove these hydrogens Gibson looked at at the polymer derived from propiolic anhydride ... 

In this instance, Ziegler-Natta polymerization yields a soluble, linear polymer 2, containing a six-membered cyclic ring fused at each repeat unit. Unfortunately, this polymer undergoes isomerization to form a non-conjugated polymer, disrupting the electronic properties of the backbone [31]. It was found that this isomerization could be prevented by the introduction of heteroatom functionality into the diyne architecture, as exemplified by the polymerization of propiolic anhydride 3, which yielded a stable polymer 4 as shown in Scheme 11 [32]. 

Another example is poly(propiolic anhydride), which was easily synthesized from the corresponding diacetylene. Though this polymer is soluble and relatively stable to air oxidation, the polymer had a low molecular weight and underwent a side reaction with the solvent.2 ... 

In an attempt to alleviate the oxidative problem encountered with polyacetylene and poly-1,6, we have examined the cyclopolymerization of propiolic anhydride ( ) to polymer 4. This process was reported to yield polymer of molecular weights up to 25000 (200 double bonds) by anionic cyclopolymerization using nucleophiles such as I, CNS, Cl in dime thy Iformamj e(DMF) and by coordination polymerization using PdCl2 in DMF. 

Propiolic acid, 58,43 Propionaldehyde, 58, 80, 82 Propionic anhydride, 57, 111 Propionyl chloride, 58, 85... 

The traditional synthesis of miinchnones involves the cyclodehydration of N-acylamino acids usually with acetic anhydride or another acid anhydride. Potts and Yao (3) were apparently the first to employ dicyclohexylcarbodiimide (DCC) to generate mesoionic heterocycles, including miinchnones. Subsequently, Anderson and Heider (4) discovered that miinchnones can be formed by the cyclodehydration of N-acylamino acids using Ai-ethyl-Ai -dimethylaminopropylcarbodiimide (EDC) or silicon tetrachloride. The advantage of EDC over DCC is that the urea byproduct is water soluble and easily removed, in contrast to dicyclohexylurea formed from DCC. Although the authors conclude that the traditional Huisgen method of acetic anhydride is still the method of choice, these two newer methods are important alternatives. Some examples from the work of Anderson and Heider are shown. The in situ generated miinchnones (not shown) were trapped either with dimethyl acetylenedicarboxylate (DMAD) or ethyl propiolate. 

Padwa et al. (75) found that the unsymmetrical miinchnone 137, which was generated from A-acetyl-7/-benzylglycine (136) and refluxing acetic anhydride, reacts with methyl propiolate to give an 8 1 mixture of pyrroles 138 and 139. The same product ratio is obtained from the reaction of methyl propiolate and the azomethine ylide derived from 7/-benzyl-A(-(a-cyanoethyl)-A(-[(trimethylsilyl)-methyl] amine. 

Despite the uncertainties regarding regiochemistry, the reaction of propiolates with miinchnones has found use in synthesis. Kane and co-workers (84) synthesized the calcium channel activator FPL 64176 (161) using a mtinchnone cycloaddition protocol. Thus, reaction of amino acid 158 with acetic anhydride in the presence of acetylenic dipolarophUe 159 gave pyrrole 160 in 49% yield. Base-induced elimination of the 4-nitrophenethyl protecting group afforded FPL 64176 (161) in 85% yield. 

Other methods of preparing flavone include the action of ethanolic alkali on 2 -acetoxy-a,/3-dibromochalcone 7 Claisen condensation of ethyl o-ethoxybenzoate and acetophenone, and cyclization of the resulting 1,3-diketone with hydriodic acid 8 and treatment of 3-bromoflavanone with potassium hydroxide in ethanol.9 Flavone has also been prepared from ethyl phenyl-propiolate by condensation with sodium phenoxide and subsequent cyclization with phosphorus pentachloride in benzene 10 by fusing o-hydroxyacetophenone with benzoic anhydride and sodium benzoate 11 by the dehydrogenation of 2 -hydroxychal-cone with selenium dioxide 12 and by the action of alkali on flavylium chloride.13... 

Attempts to isolate 2,3-dimethoxyfuran (156) have, as yet, been fruitless (79JCS(P1)1893), but it may be generated in situ and trapped with the propiolate (155) the initial adducts (157) are unstable under the acidic conditions and yield the biphenyls (158) and (159) (Scheme 67). 2,5-Bis(trimethylsilyloxy)furans, readily available from succinic anhydrides in one step, are also more reactive than furan in Diels-Alder reactions (80TL3423). They readily undergo reaction with both DMAD and ethyl acrylate. Thus at 50 °C in carbon tetrachloride the furan (160) with DMAD followed by detrimethylsilylation gave only the quinone (163). At 80 °C, however, the hydroquinone (164) is the major product. Both the intermediates (161) and (162) may be detected by ]H NMR spectroscopy. The formation... 

Dihydro-1,3-thiazine derivatives (208) and (210) are prepared by the addition of alkyl propiolates to thioureas and dithiocarbamic acids respectively. In the latter case it is necessary to cyclize the initial products (209) with acetic anhydride (Scheme 96) (70AJC51). Ring expansion of isothiazolium chlorides (211) by the action of potassium cyanide provides a route to imine derivatives (212 Scheme 97) (79TL1281). 

The 1,3-dipolar cycloaddition between quinoline-1-oxide (346) and methyl propiolate in the presence of acetic anhydride and hydroquinone gave 348 via 347.390... 

Keywords (alkoxyphenyl)propiolic acid, Diels-Alder reaction, anhydride... 

There is no easy and/or effective method for the preparation of 1,2,3,4-tetrasubstituted naphthalenes starting from a simple naphthalene derivative and based on classical substitution methodology. A clever new route, based on the now common concept of "tandem" reactions, is illustrated as follows. Heating of the sulfoxide 1 with acetic anhydride at 120°C in the presence of maleic anhydride gave an adduct 2, C20H16O4S, in 87% yield as a mixture of diastereomers. Reaction of the adduct 2 with PTSA in THF at 25°C gave the naphthalene derivative 3 in quantitative yield. Use of methyl propiolate in place of maleic anhydride did not result in isolation of an adduct the product was the tetralone 4 (51%). 

Methyl l-hydroxynaphthalene-2-carboxylate is formed in 19% yield when homophthalic anhydride and methyl propiolate are heated in toluene at 150° for 24 hours. 

From the reaction with dimethyl fumarate, the 1 1 cycloadduct 471 was also isolated. On oxidation with 2,3,5,6-dichlorodicyanobenzoquinone in boiling dioxane, dihydropyrrolo[l,2-fl]quinazoline-l-carboxylate (473) afforded the pyrrolo(l,2-a]quinazoline-l-carboxylate 474. The latter product also resulted when the acid 475 was treated with an excess of ethyl propiolate and acetic anhydride in boiling xylene. The reaction of the thiazo[3,2-c]quinazoline 469 with dimethyl acetylenedicarboxylate in boiling toluene led to the pyrimido[l,2-a]quinazolinone 472. 

Methylpodocaipic acid, 42 Methyl propiolate, 547 Methyl propynoate, 220 N-Methylpyrrolidine, 345, 355,462,463 Methyl sterculate, 436 a-Methylstyrene, 493 /3-Methylstyrene, 71, 292 Methylsuccinic anhydride, 357... 

Propene, 226 0-Propiolactone, 530, 957 Propiolic acid, 712 Propionaldehyde, 225, 279, 515 Propionic anhydride, 196 Propionyl chloride, 50, 388, 389... 

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