Reaction of alkynes with

Aikynes undergo a variety of reactions using either Pd(H) or Pd(0), and they are treated separately oxidative reactions of alkynes with Pd(Il) are treated in Chapter 3, Section 8. Pd(0)-catalyzed reactions of alkynes with halides in Section 1.1.2 in this chapter, and other reactions in this section. 

When formulating a mechanism for the reaction of alkynes with hydrogen halides we could propose a process analogous to that of electrophilic addition to alkenes m which the first step is formation of a carbocation and is rate determining The second step according to such a mechanism would be nucleophilic capture of the carbocation by a halide ion... 

Formation of Sulfides. Thiols react readily with alkenes under the same types of conditions used to manufacture thiols. In this way, dialkyl sulfides and mixed alkyl sulfides can be produced. Sulfides are a principal by-product of thiol production. Mixed sulfides can be formed by the reaction of the thiol using a suitable starting material, as shown in equations 21, 22, and 23. Vinyl sulfides can be produced by the reaction of alkynes with thiols (38). 

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 ... 

Further details must be added for a complete description, but these outlines encompass most reactions of alkynes with simple electrophiles. 

Reactions of alkynes with trinuclear group 6-group 9 clusters incorporating bridging alkylidyne ligands proceeded by coupling the C-donor ligands. 

Another example of the addition of terminal alkynes to C=N in water is the coupling of alkynes with in-situ-generated A-acylimines (Eq. 4.32) and A-acyliminium ions (Eq. 4.33). In 2002, Li et al. developed a coupling reaction of alkynes with A-acylimines and A-acyliminium ions mediated by Cu(I) in water to generate propargyl amide derivatives.57 Either an activated imine derivative or imininum derivative was proposed as the intermediate, respectively. 

Benzo-fused pyrrolizines can be prepared from the palladium-catalyzed reaction of alkynes with imines of 2-halogenoanilines. Pyrimidine-substituted alkynes react in the same way, to produce the pyrimidine-fused pyrrolizines 161 <2001JOC412> (Scheme 48). 

A potentially useful synthesis of 177-1,2-azaphospholes by the reaction of alkynes with l-aza-2-phospha-4-vanada-2-cyclobutenes generated from R1N=VC13 and phosphaalkynes may be considered as an example of cyclic carbovanadation 4 (Scheme 50). 

Most probably, Zr-catalyzed C—C bond formation by cyclic carbozirconation was first observed in 1978, when the Zr-catalyzed reaction of alkynes with Et3Al was reported [13,56]. An acyclic carbozirconation mechanism similar to that of methylalumination was initially... 

The reaction of alkynes with AIX3 at —78 °C has been shown, by NMR spectroscopy, to generate a zwitterionic cr-cyclobutadiene aluminum species 225 (Scheme 58)211a. Transfer of the cyclobutadiene ligand from 225 to a variety of transition metals has been reported211. 

While one of the first preparations of a cyclobutadiene-metal complex involved the cyclodimerization of diphenylacetylene in the presence of Fe(CO)5 at high temperature212, the thermal reaction of alkynes with Fe(CO)s gives predominantly cyclopentadienone complexes (Section IV.E.l.b). The cyclization of alkynes by a wide variety of metal complexes has been reported (Scheme 59)l 5-21 A—222... 

The intermolecular reaction of alkynes with acylcarbene complexes normally yields cyclopropenes [587,1022,1060-1062]. Because of the high reactivity of cyclopropenes, however, in some of these reactions unexpected products can result. In particular intramolecular cyclopropanations of alkynes, which would lead to highly strained bicyclic cyclopropenes, often yield rearrangement products of the latter. In many instances these products result from a transient vinylcarbene complex, which can be formed by two different mechanisms (Figure 4.3). 

Vinyltellurides with E configuration were obtained by the reaction of alkynes with DIBAL-H followed by the addition of an organotellurenyl bromide in the presence of dry LiCl." ... 

Cross-coupling reactions of alkynes with (Z)-vinylic tellurides under PdCyCuI catalysis gives rise to the corresponding enynes and enediynes with retention of the configuration."... 

The reaction of alkynes with nitric acid or mixed acid is generally not synthetically useful. An exception is the reaction of acetylene with mixed acid or fuming nitric acid which leads to the formation of tetranitromethane. A modification to this reaction uses a mixture of anhydrous nitric acid and mercuric nitrate to form trinitromethane (nitroform) from acetylene. Nitroform is produced industrially via this method in a continuous process in 74 % yield. " The reaction of ethylene with 95-100 % nitric acid is also reported to yield nitroform (and 2-nitroethanol). The nitration of ketene with fuming nitric acid is reported to yield tetranitromethane. Tetranitromethane is conveniently synthesized in the laboratory by leaving a mixture of fuming nitric acid and acetic anhydride to stand at room temperature for several days. ... 

The reaction of alkynes with dinitrogen tetroxide is less synthetically useful as a route to nitro compounds. The reaction of 3-hexyne with dinitrogen tetroxide yields a mixture of cis- and fran -3,4-dinitro-3-hexene (4.5% and 13% respectively), 4,4-dinitro-3-hexanone (8%), 3,4-hexanedione (16%) and propanoic acid (6%). 2-Butyne forms a mixture containing both cis- and fran -2,3-dinitro-2-butene (7 % and 34 % respectively). " ... 

In some cases, it is possible to promote the Diels-Alder-type reaction. We have found that in the presence of polar auxiliary ligands (stabilizer), the Co-mediated reaction of alkynes with activated C,C or C,0 double bonds takes place (87MI6). These findings are only understandable if there is a direct interaction between the cp-cobaltacyclopentadiene and the polar stabilizer, which may act by blocking free coordination sites at the Co [Eq.(45)]. 

Scheme 10 Arylation reaction of alkynes with Ph3BiF2...

Although much emphasis has been placed on the importance of alkene metathesis in organic synthesis, alkyne metathesis is also significant. Metathesis reactions of alkynes with alkencs and metathesis reactions of alkynes with alkynes have both been carried out efficiently. 

Reactions of alkynes with xenon difluoride have not been widely investigated. Propyne reacts more slowly with xenon difluoride in the absence of a catalyst than propene, to form a complex product mixture with 33% 2,2-difluoropropene.26 Diphenylethyne treated with xenon difluoride in the presence of hydrogen fluoride forms 1,2-diphenyltctrafluoroethane in 50% yield, comparable yields of 1,2-dialkyltetrafluorocthanes are observed on treatment of 1,2-dialkyl-propenes with xenon difluoride in dichloromethane at room temperature.58... 

Compound (157) is formed from (158) by oxidation. 2-Vinylpyridines (160) on treatment with DMAD yield indolizines (161). A collection of reactions of alkynes with pyridines has been presented (76S209). 

Silylstannylation is also observed in the Pd(PPh3)4-catalyzed reaction of alkynes with disilanyl stannanes, in which both Si-Si and Si-Sn bonds are present. The alkynes undergo insertion into the Si-Sn bond, to regio-and stereoselectively yield (/8-disilanylalkenyl)stannanes [Eq. (25)].73 With terminal alkynes, the stannyl group adds regioselectively to the internal carbon atom. Aliphatic alkynes are not reactive in this system. 

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