Alkyl halides, reaction with aluminum

Organoaluminum sonochemistry is not yet well developed despite the synthetic and economic interest. Aluminum, a ductile metal, is easily activated by sonication, as evidenced by the use of foils to determine the energy of cleaning baths. Alkyl halides react with aluminum at room temperature in THF to give the sesquihalide, reduced to the trialkyl compound in the presence of magnesium. Examples are known with bromomethane or -ethane.1 2,183 reaction occurs with stirring under similar conditions. Triethylaluminum was used in sonochemical transmetallation reactions leading to zinc and boron alkyls (Eq. 38). 

Partially fluorinated vinyl ethers of fluoroolefins are quite susceptible to the action of Lewis acids. Reaction usually proceeds with ionization of the allylic C-F bond and results in formation of C=0 group and elimination of alkyl halide. Indeed, 3-chloro-2-methoxyhexafluoro-2-butene 82 reacts with A1C13 with formation of trichlorovinyl ketone 83, and cyclic alkoxyfluoroalkenes demonstrate similar behavior in reaction with aluminum or tin(IV) halides [170] ... 

Other preparative routes to aluminum alkyls include reaction of aluminum halides with organometallic reagents such as lithium alkyls (Equation (3)). 

In order to prepare organoaluminum compounds with specific functional groups in the alkyl radical, reactions of aluminum halides with various metallic compounds are particularly important. Thus, vinyl magnesium halides and aluminum trichloride give unstable trivinylalane (see Section III,B,2) (17, 288) ... 

Alkyl fluorides are the most reactive of the alkyl halides. Boron trichloride (BCI3), boron trifluoride (BF3), boron triiodide (BI3), and boron tribfomide (BBr3) all catalyze the reaction of alkyl fluorides and benzene, although they are ineffective catalysts for the analogous reaction of alkyl chlorides and alkyl bromides. reaction with mixed halides, the C—F bond reacts faster than the C—Cl, C—Br or C—I bond. This is consistent with the observed order of reactivity for alkyl halides with aluminum chloride (AICI3) ... 

In the concerted process, the benzene ring reacts with the alkyl halide-aluminum chloride complex to form the alkylated benzene. In this mechanism, there is no carbocation rearrangement because there is no free carbocation stage. In the two step process, however, there is a free carbocation stage. The alkyl halide complexes with the aluminum chloride. This complex breaks down to form the free carbocation, which can then undergo rearrangement to form a more stable species. The benzene ring can then react with the carbocation to form the alkylated benzene. Therefore, reactions (a), (b) and (c) must have followed the two step mechanism that is, the c-arbocation mechanism. 

In a Friedel-Crafts reaction, alkyl halides react with benzene in the presence of aluminum chloride to give an alkylbenzene. It is one of the most useful synthetic methods in organic chemistry. 

Alkylation of benzene with alkyl halides m the presence of aluminum chloride was discovered by Charles Friedel and James M Crafts m 1877 Crafts who later became president of the Massachusetts Institute of Technology collaborated with Friedel at the Sorbonne m Pans and together they developed what we now call the Friedel-Crafts reaction into one of the most useful synthetic methods m organic chemistry... 

Triflates of aluminum, gallium and boron, which are readily available by the reaction of the corresponding chlorides with triflic acid, are effective Fnedel-Crafis catalysis for alkylation and acylation of aromatic compounds [119, 120] Thus alkylation of toluene with various alkyl halides m the presence of these catalysts proceeds rapidly at room temperature 111 methylene chloride or ni-tromethane Favorable properties of the triflates in comparison with the correspond mg fluorides or chlorides are considerably decreased volatility and higher catalytic activity [120]... 

Tin alkyl hydrides can be prepared from the halides by the reaction with lithium aluminum hydride. 

The second pathway is represented by Eqs. (8)—(11). These reactions involve reduction of the Nin halide to a Ni° complex in a manner similar to the generation of Wilke s bare nickel (37, 38) which can form a C8 bis-77-alkyl nickel (17) in the presence of butadiene [Eq. (9)]. It is reasonable to assume that in the presence of excess alkyaluminum chloride, an exchange reaction [Eq. (10)] can take place between the Cl" on the aluminum and one of the chelating 7r-allyls to form a mono-77-allylic species 18. Complex 18 is functionally the same as 16 under the catalytic reaction condition and should be able to undergo additional reaction with a coordinated ethylene to begin a catalytic cycle similar to Scheme 4 of the Rh system. The result is the formation of a 1,4-diene derivative similar to 13 and the generation of a nickel hydride which then interacts with a butadiene to form the ever-important 7r-crotyl complex [Eq. (11)]. 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Reactions, e.g., with alkyl halides in ether using Ziegler-Natta catalyst form alkyl aluminum halides, R3AI2X3, [R2A1X]2 and [RA1X]2 with bromine vapor forms anhydrous aluminum bromide,... 

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