Acetylene condensation reactions

These processes have supplanted the condensation reaction of ethanol, carbon monoxide, and acetylene as the principal method of generating ethyl acrylate [140-88-5] (333). Acidic catalysts, particularly sulfuric acid (334—338), are generally effective in increasing the rates of the esterification reactions. Care is taken to avoid excessive polymerisation losses of both acryflc acid and the esters, which are accentuated by the presence of strong acid catalysts. A synthesis for acryflc esters from vinyl chloride (339) has also been examined. 

The chemistry of 1,2,5-thiadiazole systems (RC)2N2S has been extensively investigated. " In addition to the condensation reactions of sulfur halides with 1,2-diaminobenzenes, this ring system is obtained in high yields by the reaction of S4N4 with acetylenes (Section 5.2.6). For example, the reaction of S4N4 with diphenylacetylene produces 3,4-diphenyl-1,2,5-thiadiazole in 87% yield. 

The Fiesselmann thiophene synthesis involves the condensation reaction of thioglycolic acid derivatives with a,P-acetylenic esters, which upon treatment with base results in the formation of 3-hydroxy-2-thiophenecarboxyIic acid derivatives. 

The reactivity of arylhalides in the acetylenic condensation sharply decreases in the series Ar—I, Ar—Br, Ar—Cl. The rate of reaction of phenylacetylene with iodo derivatives is 800 times higher than that of the reaction with bromo derivatives and is 10 higher than that of the reaction with corresponding chlorides (75JOM253). Taking into account the very low activity of halogenopyrazoles (66AHC347), the catalytic variant of acetylenic condensation mainly involves the most active iodo derivatives. 

The high reactivity of monosubstituted acetylenes in many reactions (acetylenic condensation, Favorsky reaction, Mannich reaction, oxidative coupling, etc.) is determined by their acidity (7IMI1 83MI1). The literature data on the thermodynamic CH acidity of these compounds are rather scarce. 

The successful synthesis of 2-thienyl and substituted 2- and 3-thienyl-acetylenes in yields as high as 60-80% opened a wide variety of synthetic applications. Various addition reactions with carbonyl compounds or epoxides could be carried out with ease. Aliphatic as well as aromatic amine addition reactions, or condensation reactions with hydrazine or hydroxylamine could be easily performed. 

In the area of reaction energetics. Baker, Muir, and Andzehn have compared six levels of theory for the enthalpies of forward activation and reaction for 12 organic reactions the unimolecular rearrangements vinyl alcohol -> acetaldehyde, cyclobutene -> s-trans butadiene, s-cis butadiene s-trans butadiene, and cyclopropyl radical allyl radical the unimolecular decompositions tetrazine -> 2HCN -F N2 and trifluoromethanol -> carbonyl difluoride -F HF the bimolecular condensation reactions butadiene -F ethylene -> cyclohexene (the Diels-Alder reaction), methyl radical -F ethylene -> propyl radical, and methyl radical -F formaldehyde -> ethoxyl radical and the bimolecular exchange reactions FO -F H2 FOH -F H, HO -F H2 H2O -F H, and H -F acetylene H2 -F HC2. Their results are summarized in Table 8.3 (Reaction Set 1). One feature noted by these authors is... 

Straight acetylene can be used as an explosive when in liquefied or solidified form (see Acetylene as an Explosive) (See also Acetylene Condensation or Polymerization Products, Acetylene Derivatives, Acetylene Hydroperoxides Peroxides, Acetylene-Nitric Acid Reactions, Acetylene Reactions, Acetylenic Compounds, Acetylides, Cuprene and Halogenated Acetylenes)... 

Other routes to 1,3-oxazines employ condensation reactions between /3-chloroketones and nitriles or between chloroalkyl amides and alkynes <69LA(723)ill) (Scheme 62). Thiazines are available through similar condensations between thioamides, aldehydes and acetylenes (74G849), and AH- 1,3-benzoxazines may be prepared from 2-hydroxybenzyl alcohols and nitriles in the presence of either perchloric or sulfuric acids (Schemes 63 and 64) (68MIP22700). 

Once again, condensation reactions are needed to produce more saturated species such as methyl acetylene which is produced by reactions such as... 

This reaction leads to new deoxycellulose derivatives that contain a residue of acetylenic alcohol. Like the reactions on addition of water, methanol, or diethylamiiK, the condensation reaction with acetoiK proceeds quantitatively. 

Zeiss and co-workers further found that acetylenes displace THF molecules in the coordination sphere of chromium and other metals in analogous complexes. The acetylenes subsequently condense in cyclic arrangements, and such cyclic condensation reactions have provided important new routes to both arene-metal complexes and uncomplexed arenes. Further details on these novel reactions are contained in the reviews at the end of this section. 

Ions 43+ and 44+ are characterized by substantially different bimolecular reacti-vities. While 43+ does generally not react, 44+ undergoes a variety of addition and condensation reactions. Considerable attention has been devoted to the reactions of ion 44+ with its precursor, with acetylene and with diacetylene, as such processes possibly initiate soot formation in flames . ... 

Numerous friends and colleagues in the field of metathesis (the soldiers to whom we dedicate this book) have encouraged us to believe that a new book incorporating these recent developments would be both timely and welcome. We felt, however, that the book should still outline the historical development of the subject and not just be a supplement to the original book. This has necessarily meant some compression of earlier material and some restriction of discussion. The title has been expanded to include the words Metathesis Polymerization , which embraces not only ring-opening metathesis polymerization (ROMP), but also the metathesis condensation reactions of acyclic dienes (ADMET) and the addition reactions of acetylenes. The division of the material and the subjects of the chapters follow the same pattern as before. The literature has been covered up to mid-1996. 

A variety of propargylamines can be prepared by three-component Mannich condensation of acetylenes, aldehydes, and secondary amines (Scheme 7.19) [66, 67). These reactions were performed using CuCl to activate the acetylene component. Reaction times varied from 3-36 h. Silver iodide has recently been used to catalyze the reaction [68]. 

Disubstituted quinolines of type 21 were obtained from acetylenic ketones 2 as a result of a condensation reaction with 2-amino thiophenol 19 followed by sulfur extrusion (entry f). Acetylenic ketones have also been employed as dienophiles in Carbonyl-Alkyne-Exchange (CAE) reactions with dienes 22 (derived from 2,2-dialkyl-2,3-dihydro-4//-pyran-4-ones )(entry g) or 24 (entry h) to yield aromatic compounds 23 and 25 in a highly regioselective way. 

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