1 - Halo- 2- alkenes

Halo-alkenes are common pollutants. Therefore, there is an ongoing study on plausible approaches to the dehalogenation of halo-alkanes. One of these approaches involves their electrocatalytic reduction. NinL2 + (L = a tetraaza macrocyclic ligand) complexes were proposed as plausible electrocatalysts (150). A pulse radiolytic study on the mechanism and kinetics of the reaction ... 

Furthermore, the presence of a Pd catalyst in the medium and the generation of an allylated halo alkene can be readily exploited for a subsequent Sonogashira coupling to give the dienynes 221 in good yields as a consequence of a halo-allylation-Sonogashira sequence (Scheme 92). 

Homogeneous catalysis for the reduction of alkenes is an increasingly useful synthetic tool. The stereoselectivity of the reduction is significantly better than with heterogeneous catalysts,385 which can be illustrated by the hydrogenation of 380 to the trans fused derivative 381 in 95% yield.386 Reduction of co-halo alkenes... 

Halo-alkenes are common pollutants. Therefore, there is an ongoing study on plausible approaches to the dehalogenation of halo-alkanes. One of these approaches involves their electrocatalytic reduction. 

In principle, carbonylative cyclization, that is, acylpalladation or Ac—Pd process, or noncarbonylative cyclization, that is, sample carbopalladation or C—Pd process, in the presence of CO and a Pd catalyst. Various possibilities with cyclization processes are discussed in Part VI including Sects. VI.4-VI.6. hi this section, those cases that do not incorporate CO during the cychzation processes but do so only after cyclization will be discussed. Such cychc carbopalladation-carbonylative termination tandem and cascade processes are represented by the Type II C—Pd process in Scheme 2, which may take place in competition with the other processes shown in Scheme 2, especially the cyclic Heck reaction (Type 1 C—Pd process) and cyclic carbopalladation involving cyclopropa-nation (Type 111 C— Pd process). 

Table 18, pp. 269/74, lists the reactions of linear, branched, and cyclic alkenes, halo-alkenes, and oxygen-, sulfur-, nitrogen-, and phosphorus-containing compounds with C=C double bonds, the reaction conditions, and the product distribution of the phosphanes obtained (abbreviations are explained in the footnotes at the end of the table). 

Consider a regression for a set of 66 halogenides and their boiling points [116]. The molecules considered include branched and cyclic halo-alkanes and several halo-alkenes involved as heteroatoms chlorine, bromine, and iodide. All the molecules and their boiling points, which cover the range from -24°C (chloromethane) to... 

The radical cyclizations of diacetoneglucose-derived halo-alkenes for example (66) to give cyclohexane and cycloheptane annulated furanoses has been described (Scheme 16). A paper by two of the same authors describing similar work has also appeared. ... 

Zirconocene j -imine complexes formed by a C-H activation route from a variety of amines can be trapped by [Pg.518]

The TT-allylpalladium complexes formed from conjugated dienes are reactive and react further with a nucleophile to give the 1,4-difunctionalized products 340. Based on this reaction, various nucleophiles are introduced into conjugated dienes to form 1,4-difunctionalized 2-alkenes. Acetoxy, alkoxy, halo, and... 

The best procedures for 3-vinylation or 3-arylation of the indole ring involve palladium intermediates. Vinylations can be done by Heck reactions starting with 3-halo or 3-sulfonyloxyindoles. Under the standard conditions the active catalyst is a Pd(0) species which reacts with the indole by oxidative addition. A major con.sideration is the stability of the 3-halo or 3-sulfonyloxyindoles and usually an EW substituent is required on nitrogen. The range of alkenes which have been used successfully is quite broad and includes examples with both ER and EW substituents. Examples are given in Table 11.3. An alkene which has received special attention is methyl a-acetamidoacrylate which is useful for introduction of the tryptophan side-chain. This reaction will be discussed further in Chapter 13. 

Halohydnn formation as depicted m Figure 6 13 is mechanistically related to halo gen addition to alkenes A halonium ion intermediate is formed which is attacked by water m aqueous solution... 

When we discussed elimination reactions in Chapter 5 we learned that a Lewis base can react with an alkyl halide to form an alkene In the present chapter you will find that the same kinds of reactants can also undergo a different reaction one m which the Lewis base acts as a nucleophile to substitute for the halo gen substituent on carbon... 

The formation of vicinal halohydrms from alkenes was described m Section 6 17 Halo hydrins are readily converted to epoxides on treatment with base... 

The P-halo ketone intermediates formed in the foregoing reactions arise from the capture of carbocationic intermediates by halide of the gegenions. In some cases, solvents such as acetonitrile can act as the competing nucleophilic species. For example, P-amido ketones could be obtained by the acylation of alkenes in acetonitrile (172). 

Both ( )- and (Z)-l-halo-l-alkenes can be prepared by hydroboration of 1-alkynes or 1-halo-l-alkynes followed by halogenation of the intermediate boronic esters (244,245). Differences in the addition—elimination mechanisms operating in these reactions lead to the opposite configurations of iodides as compared to bromides and chlorides. 

An alternative synthesis of (Z)-l-halo-l-alkenes involves hydroboration of 1-halo-l-alkynes, followed by protonolysis (246,247). Disubstituted ( )-and (Z)-a1keny1 bromides can be prepared from ( )- and (Z)-a1keny1 boronic esters, respectively, by treatment with bromine followed by base (248). 

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