Acidity acetylenes

Phenylpropiolic acid. This is an example of an aromatic acetylenic acid, and is made by adding bromine to the ethylenio linkage in ethyl cinnamate, and treating the resulting dibromide with alcohobc potassium hydroxide which eliminates two molecules of hydrogen bromide ... 

The shorter-chain alkynoic or acetylenic acids are common in laboratory organic syntheses, and several long-chain acids occur n ituraUy (Table 4). 

Fluoroalkyl-suhstituted acetylenic acids are more reactive dienophiles than dimethyl acetylenedicarboxylate [100] (equation 85)... 

III. Reactions of Acetylenic Acids and Esters with Individual Nitrogen ... 

Isanic) and Other Acetylenic Acids. J. Chem. Soc. [London] 1953, 1785. 

Acetylenic Acids from Fats of the Olacaceae and Santalaceae. IV. 

It occurs with the alkyls, aryls or acetylides of metals more electropositive than magnesium, but including Grignard reagents, and is often carried out by adding a solution of the organometallic compound in an inert solvent to a large excess of powdered, solid C02 it is a particularly useful method for the preparation of acetylenic acids. The Kolbe-Schmidt reaction (p. 291) is another example of carbanion carbonation. 

Standard procedure used a mixture of 0.26 mmoles acetylenic acid, 20 mg (0.005 mmoles) catalyst in acetonitrile (1.2 mol L"1) that was stirred under air atmosphere at 40°C. After completion of the reaction, the mixture was centrifugated and the solvents... 

These studies were extended to the a,/ and y-hydroxy-a,/ -acetylenic acids (61a), (81). We found that the direct carbonation of the sodium salts of thienylacetylenes or of acetylenic carbinols was of no avail even under pressure using various solvents. Small amounts of 2-thenoic acids were isolated only. However, a, -acetylenic acids as well as the... 

The free y hydroxy-acetylenic compounds in the presence of a hydroxyl group, conjugated double bond or a second triple bond is very characteristic and was observed with certain acetylenic alcohols and diacetylenic glycols in this series. 

The cis-fagaramide (J) was synthesized as outlined below. The required acetylenic acid (c) was prepared from piperonal (a) by the Corey s procedure.Treatment of piperonal with carbon tetrabromide, triphenylphosphine and zinc gave the bromo olefin (b) as an oil in 71% yield. The bromo olefin (b) was treated with 2 equivalents of n-butyl lithium followed by quenching with dry ice to give acetylenic acid (c) in 54% yield. Treatment of (c) with excess thionyl chloride without solvent at 50 followed by addition of isobutyl amine in benzene gave the acetylenic amide (d) as a viscous oil in 96% yield. Partial reduction of (d) gave cis-fagarmide (7 ) in 89% yield. 

Lithium aluminum hydride reduces acetylenic acids containing conjugated triple bonds to olefinic alcohols. Acetylenedicarboxylic acid gave, at room temperature after 16 hours, 84% yield of /ra s-2-butene-l,4-diol [975]. 

A second approach (472) to 512 started with trans-2-buitnc epoxide (524) (Scheme 67). Opening of the epoxide ring of 524 with lithium acetylide gave an acetylenic alcohol, which was converted to the acetylenic acid (525) by carbox-ylation with gaseous carbon dioxide. Partial hydrogenation of 525 followed by lactonization afforded the a,3-unsaturated lactone (526) which was transformed to the nitrolactone (527) by a Michael addition reaction of nitromethane. The Nef reaction of 527 gave the tetrahydrofuranyl acetal (528) which was converted to... 

Mercaptoacetone reacts with methyl propiolate to give a 1 1 adduct, which then cyclizes to a substituted thiophene. Similar addition reactions of mercaptans with acetylenic acids have also been reported by Owen and Sultanbawa. ... 

Thiophenols undergo base-catalyzed, Michael addition to acetylenic acids and esters to give trans addition products. These vinyl thioethers have been used in the synthesis of thiochromones. " Recently, Undheim and Lie have shown that thiophenol adds to DMAD with concomitant cyclization to give benzo[6]thiophenes. 

Substituted cyclopropyl rings conjugated with a triple bond system have recently received attention as C5 building blocks. The procedure described here is a modification of the decarboxylation-elimination reaction for the preparation of a.3 acetylenic acids from enol sulfonates of acyl malonates. Addition of aqueous alkali to the enol sulfonate of diethyl cyclopropyl carbonyl malonate gives cycl opropyl propiol ic acid, but the yield is 1 ow. 

Primary Alkyl Substitution in Acetylene Acidity of =C—H [see Problem 8.5(b)]... 

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