Halides, alkenylation

Alkyne Hydrogen halide Alkenyl cation Halide ion = X Alkenyl halide... 

Give an example of each of the following alkyl halides, alkenyl halides, and aromatic halides. 

At equilibrium, therefore, the Li becomes attached preferentially to the organic group best able to stabilize the negative charge. Hence, extensive exchanges and useful preparations are available from reaction of alkyl Li with aryl halides, cyclopropyl halides, alkenyl halides, alkynyl halides and a-heterosubstituted alkyl halides (including per- and polyhaloalkanes), but not with simple alkyl halides e.g., interaction of EtLi and Mel provides a mixture of EtLi and MeLi. 

In the example in Scheme 1.170, the TJ-alkene is formed from the -alkenyl halide. Likewise, the Z-alkene is formed selectively from the Z-alkenyl halide. Alkenyl tri-llates are also good substrates for alkylation with organocuprate reagents. Treatment of the alkenyl triflate 170 with methyl magnesium bromide and copper(I) iodide as catalyst, gave the alkylated product 171, used in a synthesis of paeonilactone A (1.171). 27... 

Compared with the carbonylation of methanol, the carbonylation of Csp3-X is relatively easier. Based on the C-X bond energy, the rate of the oxidative addition of the organic halide to an electronically unsaturated metal complex decreases along the sequence C-I > C-OTf > C-Br C-Cl C-F. In addition to (het-ero)aryl halides, alkenyl-X [52-56] and steroidal [57-62] derivatives have been successfully used as reagents in carbonylation reactions as well. 

Besides halides, alkenyl boronates and alkenyl acetates can be employed for C-H bond alkenylation under Ru catalysis. Kakiuchi and coworkers demonstrated that aromatic ketones and 2-phenylpyridines undergo regioselective alkenylation effectively on treatment with alkenyl boronates [72] and alkenyl acetates [73], respectively (Scheme 18.72 and Scheme 18.73). 

In addition to the silylation of aryl halides, alkenyl iodides can also be silylated in the presence of a palladium(O) catalyst (eq 22). This silylation proceeds stereoselectively with retention of the carbon-carbon bond stereochemistry, with neither the a-nor (Z)-isomer being produced. The byproduct that arises from this reaction is the saturated /3-aryl triethoxysilane resulting from hydrosilylative reduction of the olefin (97 3 unsaturated saturated). Interesting to note is the increased observance of this saturated byproduct in the presence of other silanes, including dimethoxymethylsilane (93 7), triethylsilane (87 13), dimethylphenylsilane (87 13) and triphenylsilane (90 10), once again demonstrating the specific advantage of triethoxysilane. The alkenylsilanes produced in this reaction are versatile intermediates that have been used effectively in other synthetic transformations. ... 

Cobalt catalysts also promote the cross-coupling reaction of aryl halides, alkenyl halides, and allyl methyl ethers to yield arylmethyl-, allyl-, and homoallyltrimethylsilanes, respectively (eq 25). ... 

We have encountered haloalkenes—alkenyl halides—as intermediates in both the preparation of alkynes by dehydrohalogenation and also the addition to alkynes of hydrogen halides. Alkenyl halides have become increasingly important as synthetic intermediates in recent years as a result of developments in organometalUc chemistry. These systems do not, however, follow the mechanisms familiar to us from our survey of the haloalkanes (Chapters 6 and 7). This section discusses their reactivity. 

A Gilman reagent couples with alkyl halides, alkenyl halides (vinyl halides), and aryl halides. 

PhR Reaction works well only with tertiary alkyl halides (alkenyl and aryl... 

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