Alkenyl and Alkynyl Halides

The most readily available alkenyl halide is chloroethene (vinyl chloride), which can be prepared by a number of routes  

The most economical commercial preparation is high-temperature chlorination of ethene. A useful modification of this process uses hydrogen chloride in place of chlorine. An oxidizing agent is required to raise the oxidation state of chlorine in HC1 to that of Cl2 molecular oxygen is used for this purpose along with cupric salts as catalysts. 

General methods of preparation for alkenyl and alkynyl halides are listed in Table 14-5. By the alkynyl halides we mean 1-halo-alkynes. One interesting method by which they may be prepared employs 1-alkynes with hypohalites  

This kind of reaction does not proceed with either alkanes or alkenes. 

Chloroethene is produced in vast quantities for the production of polymers (polyvinyl chloride) and copolymers  

---

Arylmetals can be coupled with alkenyl and alkynyl halides. In these cases, the reverse polarity affinity patterns, i.e., the alkenyl-aryl and alkynyl-aryl coupling reactions... 

Substitution of alkenyl and alkynyl halides. Replacement of the chlorides and fluorides with a methyl group in excellent yields is achieved with the cobaltate or ferrate reagent. 

Aryl-, alkenyl-, and alkynylpalladium complexes (Table 9) are generated in manners similar to the preparation of alkyl- and benzylpalladium derivatives. However, oxidative addition is much more widely applicable and satisfactory than in the preparation of alkyl-palladium derivatives, since aryl, alkenyl, and alkynyl halides are not only much more reactive toward Pd(0) complexes than their alkyl counterparts but are also uncomplicated by j8-elimination. 

Until recently, cross-coupling between alkylmetals and aryl, alkenyl, and alkynyl halides was achieved mostly with alkylcoppers. Over the past two decades, however, the Ni- or Pd-catalyzed reaction of alkylmetals with the unsaturated organic hahdes mentioned above has been developed as a viable alternative, as detailed in Sect. ni.2.II. The Cu-based methodology still remains highly competitive. So, it is advisable to consider both options for finding the method for a given case. 

The Suzuki-Miyaura reaction involves the palladium-catalyzed cross-coupling between organoboron compounds and halides. In most cases, aryl halides are used as electrophiles, but recent developments have broadened the scope and alkyl, alkenyl, and alkynyl halides can be successfully used as reaction partners. Among C—C coupling reactions, Suzuki-Miyaura reaction has become one of the most appealing because the reactants are air stable, nontoxic and tolerant of a variety of functional groups. 

Aryl, Alkenyl, Benzyl, and Alkynyl Halides, and Their Pseudo-Halides... 

Other pseudo-halides are used for carbonylation. Phenyl tluorosulfonate (484) can be carbonylated to give benzoate[337]. Aryl(aryl)iodonium salts[338], aryl(alkenyl)iodonium salts (485)[339], and arylialkynyl)iodonium salts (486)[340] are reactive compounds and undergo carbonylation under mild conditions (room temperature, 1 atm) to give aryl, alkenyl, and alkynyl esters. lodoxybenzene (487) is carbonylated under mild conditions in... 

Palladium-catalyzed carbon-carbon bond forming reactions like the Suzuki reac-tion as well as the Heck reaction and the Stille reaction, have in recent years gained increased importance in synthetic organic chemistry. In case of the Suzuki reaction, an organoboron compound—usually a boronic acid—is reacted with an aryl (or alkenyl, or alkynyl) halide in the presence of a palladium catalyst. 

Catalyst 11 showed great tolerance for functional groups like rmsaturated carbon-carbon bonds (alkenyl and alkynyl moieties), halides, electron-withdrawing and -donating groups, etc. (Table 4). 

The Suzuki Coupling, which is the palladium-catalysed cross coupling between organoboronic acid and halides. Recent catalyst and methods developments have broadened the possible applications enormously, so that the scope of the reaction partners is not restricted to aryls, but includes alkyls, alkenyls and alkynyls. Potassium trifluoroborates and organoboranes or boronate esters may be used in place of boronic acids. Some pseudohalides (for example triflates) may also be used as coupling partners. 

Alkynyl(methoxy)borates prepared in situ from an alkynyllithium or sodium and 9-methoxy-9-BBN coupled with 1-alkenyl and aryl halides (Equation (210)).899-902 Addition of triisopropylborate to lithium acetylide yielded an air stable and isolable ate complex that couples with aryl and alkenyl halides (Equation (211)).903 904 Air and moisture stable alkynyltrifluoroborates were probably the most convenient reagents that allow handling in air and coupling reactions in basic aqueous media (Equation (212)).46... 

This method applies to aryl, alkenyl, allyl and alkynyl halides as well as to alkenyl Inflates and exhibits the same selectivity profile as its stoichiometric precedent (Scheme 4). Moreover, it does not matter if the catalytic cycle is started at the Cr or Cr " stage as implied by Scheme 3. Therefore it is possible to substitute cheap and stable CrClj for the expensive and air-sensitive CrCf previously used for Nozaki reactions. In some cases other chromium templates such as [Cp2Cr or [CpCrCl2] can be employed, improving the total turnover number of this transformation even further [13, 14]. 

Physical and chemical data on the MR2L, (R = Me, Et, Ph, allyl, alkenyl, and alkynyl) and MXR(L) (R = Bu, Ph, tolyl X = halide) compounds are greatly lacking, owing to these compounds generally poor thermal stability. The aryl MXR(L) and alkynyl MR2L compounds constitute the most stable classes.The compounds decrease in stability Ba < Sr and XR(L),j compounds form most readily for — I... 

---