Carboxylation, acetylene

Diazopropyne reacts similarly with a monosubstituted acetylene to form 3(5)-alkynylpyrazoles (68LA113). Thus, the reaction of diazopropyne with acetylene-carboxylic acid methyl ether results in 5-ethynyl-l//-pyrazole-3-carboxylic acid methyl ether in 48 h in 62% yield. 5-Ethynyl-l//-pyrazole-3,4-dicarboxylic acid dimethyl ester was prepared by reaction of diazopropyne with acetylenedicar-boxylic acid methyl ether (Scheme 10). 

H. Reactions with Acetylenic Carboxylates, Acrylates, and 1,3-Dipoles... 

The stereochemistry of the addition of phosphorus pentachloride to isolated acetylenes in non-polar solvents has been shown by n.m.r. to be CIS, as illustrated for the adduct (46) from propyne. This observation has been explained in terms of a four-centre process. Contrary to a previous report, the reaction of triphenylphosphine hydrobromide with phenyl-acetylene carboxylic acid (47) yields both the trans- and the known c/5-adducts. 

The degradation of alkynes has been the subject of sporadic interest during many years, and the pathway has been clearly delineated. It is quite distinct from those used for alkanes and alkenes, and is a reflection of the enhanced nucleophilic character of the alkyne C C bond. The initial step is hydration of the triple bond followed by ketonization of the initially formed enol. This reaction operates during the degradation of acetylene itself (de Bont and Peck 1980), acetylene carboxylic acids (Yamada and Jakoby 1959), and more complex alkynes (Figure 7.18) (Van den Tweel and de Bont 1985). It is also appropriate to note that the degradation of acetylene by anaerobic bacteria proceeds by the same pathway (Schink 1985b). 

Room temperature conditions affected only the conversion, the reaction rate being smaller (entry 6). Noticeably, cyclization of 2-prop-2-ynyl-malonic acid monomethyl ester le and 2-phenyl-pent-4-ynoic acid If, also occurred with very good results (entries 7, 8). The obtained results may be ascribed to the LDH support, which exhibits enough basic properties to activate the unsubtituted acetylenic carboxylic acids. Basically, the composition of the LDH exhibits only a very minor influence in these reactions. 

In summary, the Zn-Al and Zn-Ga based-hydrotalcites were found as very effective supports for docking a Rh(TPPTS)3Cl complex. The process was carried out via ionic exchange and occurred without any damage of die support structure or of the complex. The resulted catalysts were found to catalyze the cyclization of acetylenic carboxylic acids to the corresponding 5-membered ring heterocycles in good to excellent yields. The basic properties of the support also allow a clean and selective reaction of unsubstituted acetylenic carboxylic acids. 

The zwitterions (139) (formed by the reaction of the tributylphosphine-carbon disulphide adduct with acetylenic carboxylic acids) undergo hydrolysis to give 1,3-dithioles.133 The products of alkaline hydrolysis of the salts (140) have been investigated.134... 

Esters (Sulfinates,Sulfonates, Acetates, Acetylenic Carboxylates) 300... 

Reaction XXXIV. (c) Action of Carbon Dioxide on Sodium Acetylides in Dry Ether. (B., 12, 853 J. pr., [2], 27, 417 B., 33, 3586.)—This is an example of the great activating influence of a triple bond. When carbon dioxide is passed into a solution of the sodium derivative of an acetylenic hydrocarbon in dry ether, direct addition takes place to give the sodium salt of the next highest acetylenic carboxylic acid. For example, sodium allylene yields sodium tetrolate—... 

Another method for the preparation of acetylenic carboxylates involves the reaction of 1-alkenylboranes with CO and alcohols (equation 135). The alkenyl boranes are readily prepared from alkynes by addition of boranes. PdCl2 was again the catalyst, with NaOAc as base and benzoquinone as oxidant.541... 

On the other hand, acetylenic alcohols can be electrochemically converted to the corresponding acetylene carboxylic acids in acidic electrolytes using Pb02 anodes. Processes for the synthesis of propynoic acid and acetylene dicarboxylic acid have been developed at BASF 303 - 30. ... 

For electron-poor alkynes (Scheme 2) such as acetylene carboxylic acid ethyl ester 4, the activated Au(III) catalysts lead to about 60% of the product 5 as a 3.6 1 Z/E mixture. In contrast, Au(I) complexes of phosphines activated by AgSbF6 or Lewis acids are much better suited, delivering nearly quantitative yields of 5 with complete Z-selectivity (Scheme 4) [2], Only traces of the doubly vinylated compound 6 are observed as a side product. A particularly effective Lewis acid is BF3 OEt2, which also makes the catalytic system cheaper than those using AgSbF6 as the activating agent. 

Table 2. Hydroarylation of acetylene carboxylic acid ester 4 by various arenes.3...

As delineated above, hydroarylation of electron-poor alkynes such as acetylene carboxylic acid ethyl ester 4 is best catalyzed by Au(I) complexes. In addition to the previously mentioned Ph3PAuCl/BF3-OEt2, several other Au(I)-complexes have been shown to be active catalysts, if activation by silver salts or Lewis acids is ensured [2, 4]. Remarkably, the Au(I)-precursor LAuCl can be prepared in situ by reacting AuCl with a phosphorus ligand. 

The scope and limitation of hydroarylation of acetylene carboxylic acid ester 4 using Au(I)-catalysis is revealed in Table 2. Electron-rich arenes participate well, but also furan and 2-methylfuran. p-Xylene leads to a 55 % yield, whereas an unacceptably low conversion results in the case of toluene. 

One of the most widely used methods of synthesizing TAs 16 and 17 is by condensation of thiobenzamides with acetylene mono- and dicarboxylic acids or their esters in methanol. The analogous reaction between en-aminothioamide and acetylene carboxylic acid and its esters leads to enamino-TA 18 (79JAP79 20504) (Scheme 2). 

Examples of alkylation, dealkylation, homologation, isomerization, and transposition are found in Sections 1, 17, 33, and so on, lying close to a diagonal of the index. These sections correspond to such topics as the preparation of acetylenes from acetylenes carboxylic acids from carboxylic acids and alcohols, thiols, and phenols from alcohols, thiols, and phenols. Alkylations that involve conjugate additions across a double bond are found in Section 74 (alkyls, methylenes, and aryls from olefins). 

Examples of the protection of acetylenes, carboxylic acids, alcohols, phenols, aldehydes, amides, amines, esters, ketones, and olefins are also indexed... 

Classification and Organization of Reactions Forming Difunctional Compounds. This chapter considers all possible difunctional compounds formed from the groups acetylene, carboxylic acid, alcohol, thiol, aldehyde, amide, amine, ester, ether, epoxide, thioether, halide, ketone, nitrile, and olefin. Reactions that form difunctional compounds are classified into sections on the basis of the two functional groups of the product. The relative positions... 

Cyclic active-methylene compounds react in Michael reactions not only with a,/J-unsaturated acceptors, but also with acetylene dicarboxylates, propiolates, and their derivatives (Scheme IV/8). If, for instance, acetylene carboxylic esters are added to a variety of cyclic-active methylene compounds, ring-expanded products generally are formed directly. In other cases, it is possible to isolate the intermediate cyclobutene derivatives, which can be converted to the ring enlarged compounds in a second reaction step. 

The most general methods for preparing seven- or eight-membered rings from enamines are by ring expansion of the cyclobutene, cyclobutanone or chlorocyclopro-pane adducts formed by cycloaddition of acetylene carboxylates, ketenes or chlor-ocarbenes, respectively, to enamines of cyclopentanone or cyclohexanone. These are two-carbon or one-carbon ring expansions. Three-carbon ring expansions can also be carried out by cycloaddition of activated cyclopropenes or cyclopropenones. 

Aromatization processes have also been observed in the reaction of dienamines with acetylene carboxylic esters46, ketene46fl (Scheme 30) and arynes47. 

Enol lactonization. The last step in a synthesis of ( )-cyanobacterin (2), an antibiotic isolated from a cyanobacterium, is the enol lactonization of the y,8-acetylenic carboxylic acid 1. Cyclization catalyzed by AgNO, results in the desired exocyclic y-... 

Not surprisingly, these rhodium and iridium carbene complexes were tested for their catalytic behaviour in the transfer hydrogenation of benzophenone and acetophenone (M +3), the hydrosilylation of alkynes (M +1) and also the catalytic cyclisation of acetylenic carboxylic acids (M +1). Hydrogenation works better for iridium than rhodium and for aromatic than for aliphatic ketones [40,43,44]. The iridium(I) complex is the first iridium catalyst showing activity for the cyclisation of acetylenic carboxylic acids [40]. The results for the hydrosilylation reactions were very moderate. 

These spacer-free Janus bis-carbene complexes were successfully employed in the intramolecular cyclisation of acetylenic carboxylic acids (4-pentynoic acid and 5-hexynoic acid) as well as the transfer hydrogenation of ketones and imines. 

By the oxidation of propargyl alcohol, propinol, CH=C—CH2OH (p. 167), an acid is obtained having the constitution CH=C—COOH and known as propiolic acid or propinoic acid and also as acetylene carboxylic acid. This is the simplest acid of the ethine series and the only one we shall mention. Derivatives of it are of importance in the benzene series in Part li as will be shown later. 

There have been a number of developments worthy of special mention in chemistry involving pentaco-ordinated compounds and intermediates. These include reports of molecular mechanics calculations to study the hydrolysis of cyclic phosphorus esters, further detailed studies of the reactions of tervalent phosphorus compounds with acetylene carboxylates and the first synthesis of a pentaco-ordinated phosphorus compound containing a three-membered (phosphirene) ring. There has also been further elegant work in the area of phosphatrane chemistry. 

Af-Unsubstituted pyrazoles and indazoles add to compounds containing activated double and triple bonds (67HC 22)1,B-76MI40402>. Amongst C—C double and triple bonds, maleic anhydride, acrylic acid esters and nitriles, acetylene-carboxylic and -dicarboxylic esters (78AHC(23)263), quinones, and some a,/3-unsaturated ketones have been used with success. Phenylacetylene reacts with pyrazole in the presence of Na/HMPT as catalyst to yield the Z isomer of 1-styrylpyrazole in a highly stereoselective reaction (78JHC1543). 

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