Acetylenes, addition reactions

Difluoroamino radical acetylene addition reactions, 33 185-189 addition reactions, 33 183-189 hydrogen abstraction reactions, 33 182-183 reactions with olefins, 33 183-185 reactions with other radicals, 33 181... 

Similar acetylene addition reactions take place with bis-cydopentadienylnickel carbonyl dimer (93). Changing from carbonyl to cyanide ligands seems to allow the formation of a true vinyl derivative. Thus, potassium pentacyanocobaltate, which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct XV (31). The product was thought to be the trans isomer, but the data were not conclusive. 

Generally, insertion of the alkyne into a metal-P bond is observed (Scheme 10).188,190 When aminoalkynes are used, the formation of a C=N double bond inhibits the interaction of that carbon with the metal centers of the cluster.186 187 When two PR groups are present, the alkyne has been observed to bridge between them as seen in Scheme 10.195,285 A second equivalent of diphenylacetylene can substitute for two carbonyl groups on the iron triangle.195 The hetero-main group element species Fe3(CO)9(NPh) (P Bu) and Fe3(CO)9(NPh)2 have been reacted with diphenylacetylene.273 Some of the products involved in the acetylene addition reaction are shown here (241-243). 

The first step in the soot formation mechanism is the formation of the first aromatic ring when aromatic species are not directly present in the feed. Thus, the formation mechanisms of benzene and the first aromatic species in hydrocarbon pyrolysis, particularly at high temperatures, have been investigated in great depth. Nevertheless, several uncertainties about these formation paths remain. Due to the high temperatures, acetylene addition reactions on unsaturated radicals play a key role (Frenklach and Wang, 1994) ... 

We have already discussed one important chemical property of alkynes the acidity of acetylene and terminal alkynes In the remaining sections of this chapter several other reactions of alkynes will be explored Most of them will be similar to reactions of alkenes Like alkenes alkynes undergo addition reactions We 11 begin with a reaction familiar to us from our study of alkenes namely catalytic hydrogenation... 

Addition of Hydrogen Cyanide. At one time the predominant commercial route to acrylonitrile was the addition of hydrogen cyanide to acetylene. The reaction can be conducted in the Hquid (CuCl catalyst) or gas phase (basic catalyst at 400 to 600°C). This route has been completely replaced by the ammoxidation of propylene (SOHIO process) (see Acrylonitrile). 

In the examples, a nitro group is substituted for a hydrogen atom, and water is a by-product. Nitro groups may, however, be substituted for other atoms or groups of atoms. In Victor Meyer reactions which use silver nitrite, the nitro group replaces a hahde atom, eg, I or Br. In a modification of this method, sodium nitrite dissolved in dimethyl formamide or other suitable solvent is used instead of silver nitrite (1). Nitro compounds can also be produced by addition reactions, eg, the reaction of nitric acid or nitrogen dioxide with unsaturated compounds such as olefins or acetylenes. 

An interesting approach to thermosetting acetylene-terminated polyimides via the Michael addition reaction has appeared (38). Acetylene-terminated aspartimides are readily prepared ia high yield via two routes, shown ia Figure 7. 

Cyclopentadiene contains conjugated double bonds and an active methylene group and can thus undergo a Diels-Alder diene addition reaction with almost any unsaturated compound, eg, olefins, acetylene, maleic anhydride, etc. The number of its derivatives is extensive only the reactions and derivatives considered most important are discussed. 

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). 

Both terminal and nonterminal acetylenes have been used. Activating groups oL to the acetylenic bond have included sulfone (131-135), sulfoxide (134), ester (28,133-139), and ketone (134,140). Whether adduct 183 Is designated as cis or trans depends on the investigators and the particular compound. If the addition reaction is carried out in aprotic solvents, the major isomer is 183 formed by cis addition (135,138,139). For example, the addition of aziridine to dimethyl acetylenedicarboxylate (182, X, Y = CO2CH3) in dimethyl sulfoxide (135) gave 75 % of a mixture containing 95 % of the Chester 185. Collapse of the intermediate zwitterion intermediate 186... 

The mechanism of the Fiesselmann reaction between methylthioglycolate and a,P-acetylenic esters proceeds via consecutive base-catalyzed 1,4-conjugate addition reactions to form thioacetal Enolate formation, as a result of treatment with a stronger base, causes a Dieckmann condensation to occur providing ketone 8. Elimination of methylthioglycolate and tautomerization driven by aromaticity provides the 3-hydroxy thiophene dicarboxylate 9. 

The triple bond in pyrazole derivatives gives, as do other acetylene derivatives, typical addition reactions. 

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. 

Acetylenes are of little promise in such reactions, because they require fairly drastic conditions, that is not compatible with the high explosion hazard of acetylenes. The reactions with dienes are often proceed unambiguously (1,2- and 1,4-addition) that makes it difficult to isolate individual compounds. 

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

The addition of terminal acetylenes to imines is an important reaction because of the importance of these products as building blocks. Conventionally, the addition reaction shown in Scheme 5.2 is performed with stoichiometric amounts of butyllithium in a step that is, separate from the subsequent nucleophilic addition reaction (see (b)). Carreira has recently developed a procedure that utilizes an iridium catalyst to effect the addition reaction to a wide range of aldimines and ketimines (see (a)). ... 

Highly stabilized phosphorus ylides are prepared from acetylenic esters, a carbon-based nucleophile, and triphenylphosphine in aqueous media.40 In acetone-water (2 1) solvent, the reaction proceeds via the conjugate addition of triphenylphosphine to dialkyl acetylenedicarboxy-lates the resulting vinyl triphenylphosphonium salts undergo Michael addition reaction with a carbon-nucleophile to give the corresponding highly stabilized phosphorus ylides. 

Our interest in silicon chemistry quite naturally led to a study of the hydrosilation reaction, the addition of the Si-H group across an olefin or an acetylene. This reaction is one of the most useful methods of making silicon-carbon bonds and is an important industrial process. Typically, homogeneous catalysts based on platinum, rhodium or ruthenium are used, and while very efficient, they are not recoverable(46). 

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). 

---