Alkynes halogens and

This ring may be built by the formation of a new C—C bond between alkyne and halogen functions, a reaction which is assisted by palladium dichloride-triphenylphosphtne (reviews of palladium catalysis [IMI, 3069, 3505] in the presence of piperidine (as base) and formic acid (to remove hydride ion). The reaction is regio- and stereo-selective. Replacement of the piperidine and formic acid by R-substituted tributyltin enables the R group to be transferred to the indole stereospectfically [3448]. 

Fig. 7 Node-strut topology for series of CMPs networks produced by Sonagashira-Hagihara cross-coupling chemistry [19]. The benzene nodes are shown in red. The total number of ethyne plus benzene links per strut increases in increments of one from two (CMP-0) to six (CMP-5) in this series of samples. It should be stressed that these are simple representations of the repeat unit structures for the networks. The actual three-dimensional materials have more complex structures and include both terminal alkyne and halogen end groups (see also molecular simulations, Fig. 9)...

Alkynes add either 1 or 2 moles of HBr and HCl, depending on the ratios in which the alkyne and halogen add are mixed. 

A dihaloalkene is an intermediate and is the isolated product when the alkyne and the halogen are present m equimolar amounts The stereochemistry of addition is anti... 

Similar intramolecular hydroarylations of alkynes and alkenes, which obviate the need for a halide or triflate group on the aryl ring, are now well established. Sames group screened over 60 potential catalysts and over 200 reaction conditions, and found that Ru(m) complexes and a silver salt were optimal. This process appears to tolerate steric hindrance and halogen substrates on the arene (Equations (175)—(177)). The reaction is thought to involve alkene-Ru coordination and an electrophilic pathway rather than a formal C-H activation of the arene followed by alkene hydrometallation, and advocates the necessary cautious approach to labeling this reaction as a C-H functionalization... 

Both reactions involve nucleophilic attack of tricoordinated phosphorus on tetrahedral carbon and show all the characteristics of non-polar reactants combining through polar transition states although the solvent effects are sometimes quite modest.— Subsequent studies have demonstrated nucleophilic attack on activated alkenes,Z activated alkynes,Z the carbonyl groupZ-Z and halogen , whilst in the Perkow reaction (eqn. 1) all four possible sites in... 

Halogenated organic compounds may be converted into alkenes, alkynes and allenes by various routes. 

With a combination of organic halide, alkene or alkyne, and palladium catalyst, the reaction may take a superficially similar, but different pathway other than a Heck-type reaction. In these, the halogen is retained in the products, as an alkyl or vinyl halide. These results occur when the starting organic halide is allyl, a- to a carbonyl or similar group, or attached to a perhalogenated carbon atom. In much of the early work, mixtures with Hecklike elimination products were obtained, due to elimination caused by the presence of amine bases in the reaction mixture (equation 165)323. 

Mechanism The Pd complex such as Pd(PPh3)4 activates the organic halides by oxidative addition into the carbon-halogen bond. The copper(I) halides react with the terminal alkyne and produce copper acetylide, which acts as an activated species for the coupling reactions. The oxidative addition step is followed by the transmetallation step. The proposed catalytic cycle is shown in Scheme 5.21. 

Halogens (mainly chlorine) at position 4 of quinazolines 12 can be displaced by a variety of carbon nucleophiles, c.g. carbon nucleophiles derived from active methylene compounds, ketone enolates, aromatic aldehydes, organolithium reagents, alkylidenephosphorane, dimethyloxosulfonium methylide, alkynes, and cyanide. ... 

In general, allenes are prepared by the same types of reactions which lead to alkenes elimination of hydrogen halides, halogens and water from adjacent carbon atoms. However, some methods are characteristic of allene synthesis, e.g. the dehalogenation of gem-dihalocyclopropanes, rearrangement of alkynes and the 1,4-addition to vinylalkynes. 

In contrast to the carbonylation of alkynes, the advantages of nickel as the catalyst metal are much less pronounced with alkenes. As a result, various catalytic systems have been developed. They can be roughly subdivided into two classes, i. e., halogen-containing and halogen-free. So far, none of these catalyst systems has achieved industrial significance. 

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