Addition reactions of acetylenes

Intermolecular [3 + 2]-addition to a triple bond The [3+ 2]-addition reactions of acetylenes with nitrones never afford normal adducts instead, they produce the corresponding aziridines (381). An analogous situation is observed for most of nitronates (93, 95, 382 (Scheme 3.132). 

Harmata et al. have developed a tandem Sonogashira/nitrogen-addition reaction of acetylenes 261 to sulfonamide 262 to prepare S(vi)-oxidized compounds 263 and 264 (Scheme 36) <20050L143>. When R = alkyl (e.g., Pr"), the 1,2-thiazine 263 is the major product (70%) formed via a endocyclization process, along with a minor amount (20%) of exocyclized product 264, while the five-membered ring product 264 (81%) is preferred when R= Ph. 

Vinylsilanes are proper compounds which have won great appreciation as facile intermediates for many sorts of application. They are prepared either by addition reactions of acetylenes (vide supra) or by elimination reactions of saturated organosilanes. The main reactions, carried out with vinylsilanes, are addition reactions to obtain saturated organosilanes or electrophilic substitutions of the silyl group under Friedel-Crafts conditions where a rapid cleavage of the silyl moiety occurs (Scheme 8). 

Only alkylations of acetylenes (equation 128) are covered in this section, whereas the addition reactions of acetylenes to carbonyl compounds are not. Alkylation of a terminal acetylene is effected by the reaction of an alkyl or aryl halide with the... 

The search is on for catalysts to replace those containing toxic heavy metals. The addition of hydrogen chloride to acetylene to form vinyl chloride is catalyzed by mercuric chloride. Rhodium (III) chloride on activated carbon works just as well and is much less toxic 97 It should be tried also in other addition reactions of acetylene as well as in trans-esteriflcation reactions of vinyl acetate. The reduction of 2 ethyl-2-hexenal to 2-ethylhexanol can be catalyzed by a mixture of copper, zinc, manganese, and aluminum oxides in 100% yield.98 This is said to be a replacement for carcinogenic copper chromite. In Reaction 4.15, the amount of toxic chromium(II) chloride has been reduced from stoichiometric to catalytic (9-15 mol% chromium(II) chloride) by the addition of manganese metal.99... 

The triple bonds in cyclic alkynes can, of course, be subjected to all known addition reactions of acetylenes. Here, we will discuss examples which either lead to particularly interesting addition products or demonstrate unusual reactivity of bent triple bonds. 

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. 

Pinna, G.A., M.A. PMsi, and G. Paglietti. 1990. Addition reactions of acetylenic esters upon 6-substituted-a-tetralone ketoximes and conversion of the adducts into 4,5-dihydro-l//-benz[g]indoles. J Chem Res Synopses 11 360-361. 

Isoxazole-3-carbaldehyde has been obtained as a minor product from the reaction of acetylene with a mixture of nitric oxide and nitrogen dioxide (61JOC2976). Although 3-aryl-4-formylisoxazoles have been synthesized in good yields from the reaction of benzonitrile Af-oxides with 3-(dimethylamino)-2-propen-l-one (71S433), the parent member of the series, isoxazole-4-carbaldehyde, has never been reported. It may possibly be obtained by the addition of fulminic acid to 3-(dimethylamino)-2-propen-l-one. 

Reactions of alkynes with electrophiles are generally similar to those of alkenes. Because the HOMO of alkynes (acetylenes) is also of n type, it is not surprising that there IS a good deal of similarity between alkenes and alkynes in their reactivity toward electrophilic reagents. The fundamental questions about additions to alkynes include the following. How reactive are alkynes in comparison with alkenes What is the stereochemistry of additions to alkynes And what is the regiochemistry of additions to alkynes The important role of halonium ions and mercurinium ions in addition reactions of alkenes raises the question of whether similar species can be involved with alkynes, where the ring would have to include a double bond ... 

Tlie addition reactions of allylic and acetylenic alcohols produce compounds resulting from rearrangements [16, 17] (equation 7). 

Chiral modification of diorganomagnesium compounds with the dilithium salt oi (S)-l,l -bi-naphthalene-2,2 -diol gave reagents with the empirical formula 30. Good to excellent enantiose-lectivities were observed in addition reactions of aliphatic and aromatic reagents to aromatic aldehydes30,31, however, the selectivities were not satisfactory with allylic, vinylic and acetylenic reagents. 

Once again, there is a remarkable lack of quantitative data on addition reactions of substituted acetylenes. This area is one which certainly merits investigation. 

Vinyl cations also have been invoked as intermediates in the addition of carbonium ions generated in strong acid to acetylene (50-53). Sasaki et al (50) observed 1-adamantyl methyl ketone, 25, as the sole product in the reaction of acetylene with 1-bromoadamantane in concentrated H2SO4 at 5°. Bott (51), on the other hand, reported a mixture consisting of 75% 1-adamantylacetaldehyde,... 

The addition reaction of alkyl and/or phenyl substituted silicon hydrides to acetylenes has limitations mainly due to the hydrogen donation step (cf. Scheme 5.1). Reaction (5.17) shows that the replacement of Ph by MesSi group in silanes made the reaction easier, the effect being cumulative. Indeed, the reaction time decreased from 88 h for PhsSiH to 3h for (TMS)3SiH [39], together with the amelioration of yields, and a slightly better cis stereoselectivity. 

The reactions of acetylene, including its polymerisation, that occur in the presence of cupric chloride solution have been studied 670) in the (additional) presence of biguanide dihydrochloride. This solution has the unique property of promoting the formation of acetic acid from acetylene. 

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... 

Later authors established the approximate composition of products formed in the reaction of acetylene with sulfur at different temperatures. At 325° the composition was found to be CSj 77%, thiophene 9%, thienothiophene 1 6% at 500°, CSj 77%, thiophene 12%, and thienothiophene 1 6% at 650° CS2 83%, thiophene 5%, and thienothiophene 1 3%, with sulfur conversion being 38%, 74%, and 77%, respectively. When studying this reaction at 290°-390°, Bhatt et isolated thiophenol in addition to the above compounds but failed to increase the yield of thienothiophene 1. 

Numerous reactions of acetylenic esters are reported in the literature, and many of these lead to heterocyclic compounds. Acetylenic esters undergo very facile addition reactions with several nucleophiles and also they participate as dipolarophiles in 1,3-dipolar cycloadditions, and as... 

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. ... 

Krespan and McKusick have studied the addition reaction of dithietenes to various oleflnes and acetylenes. Thus, the reaction of 3,4-bis(trifluoromethyl)-l,2-dithiete (378) with DMAD gives a dithiin derivative (379), which loses sulfur on heating to give 2,5-dicarbomethoxy-4,5-bis(trifluoromethyl)thiophene (380) [Eq. (57)]. 

The Michael addition reaction of dimercaptodiphenylether with N-(3-ethynyl phenyl) maleimide allowed the synthesis of ethynyl-terminated imido-thioether as shown in Fig. 50 (139). This acetylene terminated imidothioether was blended with acetylene terminated polyarylene ether oligomers of different molecular weights and tested as composite resins (140). Blends of functionalized thermoplastics such as the acetylene terminated polyarylene ethers with brittle high-Tg imide resins are finding increased attention for tough high-Tg composites. 

High temperature, pressure, and catalyst are required to achieve addition of ammonia to alkynes. Acetylene and ammonia yield a complex mixture of heterocyclic nitrogen bases.311,312 Ethylideneimines, thought to form through the intermediate enamines, are the products of the reaction of acetylene with primary alkylamines in the presence of catalysts.313... 

It is generally agreed that the kinetics and the distributions of deuter-ated products from the reactions of alkynes or alkadienes with deuterium are satisfactorily interpreted in terms of the consecutive addition of two hydrogen atoms, of unspecified origin, to the adsorbed hydrocarbon to yield the monoolefin. The identity of the distributions of deuteroethyl-enes from the reaction of acetylene with equilibrated and non-equil-ibrated hydrogen—deuterium mixtures also provides strong evidence for such a mechanism [91]. 

One of the characteristic features of the metal-catalysed reaction of acetylene with hydrogen is that, in addition to ethylene and ethane, hydrocarbons containing more than two carbon atoms are frequently observed in appreciable yields. The hydropolymerisation of acetylene over nickel—pumice catalysts was investigated in some detail by Sheridan [169] who found that, between 200 and 250°C, extensive polymerisation to yield predominantly C4 - and C6 -polymers occurred, although small amounts of all polymers up to Cn, where n > 31, were also observed. It was also shown that the polymeric products were aliphatic hydrocarbons, although subsequent studies with nickel—alumina [176] revealed that, whilst the main products were aliphatic hydrocarbons, small amounts of cyclohexene, cyclohexane and aromatic hydrocarbons were also formed. The extent of polymerisation appears to be greater with the first row metals, iron, cobalt, nickel and copper, where up to 60% of the acetylene may polymerise, than with the second and third row noble Group VIII metals. With alumina-supported noble metals, the polymerisation prod-... 

Metallation of alkynylcyclopropanes at the acetylenic end is accomplished either by deprotonation or via metal-halide exchange reaction with strong bases. Metallation of ethynylcyclopropane may be affected by KOH in DMF, ethereal EtMgBr or preferably BuLi in THF (equation 151)231. All three metal acetyl ides react with methyl ketones to give the corresponding alcohols. However, the instability of cyclopropyl ketones towards bases, especially at the reaction conditions required by KOH (20 °C, 6h), and the sensitivity of cyclopropenyl double bonds in cyclopropenyl ketone derivatives towards addition reactions of alkylmagnesium compounds, make the alkyllithium (-78 °C, instant reaction) superior to the other reagents. 

Hatakeyama et al. [115] have also carried out detailed product studies in the HO-initiated oxidation of the alkynes both in the presence and in the absence of NOx. The major products consisted of a-dicarbonyl compounds, i.e., HC(0)CHO from acetylene, CH3C(0)CH0 from propyne and CH3Q0)C(0)CH3 from 2-butyne, as well as HC(0)OH from acetylene and propyne and CH3C(0)OH from 2-butyne. The formation of these products was attributed to 02-reactions of the hydroxyvinyl radicals resulting from the addition reaction of HO with the alkynes, e.g.,... 

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