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Alkyl halides are reduced by samarium(II) iodide to the corresponding alkanes. The conditions of the reduction are compatible with a variety of functional groups, including alcohols, arenes, alkenes, and esters. Aryl halides are reduced to the corresponding halogen-free aromatic compounds. [6] (8)
Alkylation of enolates generated through the reduction of monohalo ketones is limited to the most reactive alkyl halides. [14] However, reduction in the presence of an aldehyde leads to reductive aldol products, analogous to the Reformatsky reaction of haloesters.
Traditionally, alkyl halides are substrates for dehydrohalogenations. The alkyl halide must be able to form an alkene, thus halides having no C–H bond on an adjacent carbon are not suitable substrates. Aryl halides are also unsuitable. Upon treatment with strong base, chlorobenzene dehydrohalogenates to give phenol via a benzyne intermediate.
Lithium aluminium hydride also reduces alkyl halides to alkanes. [36] [37] Alkyl iodides react the fastest, followed by alkyl bromides and then alkyl chlorides. Primary halides are the most reactive followed by secondary halides. Tertiary halides react only in certain cases. [38] Lithium aluminium hydride does not reduce simple alkenes or arenes.
The table below summarizes the reductions that may be carried out with a variety of metal aluminium hydrides and borohydrides. The symbol "+" indicates that reduction does occur, "-" indicates that reduction does not occur, "±" indicates that reduction depends on the structure of the substrate, and "0" indicates a lack of literature information.
To increase the range of viable substrates, Kornblum later added a preliminary conversion of the halide to a tosylate, which is a better leaving group, to the protocol, and using pyridine-N-oxide or similar reagents rather than DMSO. [5] The Ganem oxidation built on this latter modification, expanding on the use of various N-oxide reagents.
In organic chemistry, the Wurtz reaction, named after Charles Adolphe Wurtz, is a coupling reaction in which two alkyl halides are treated with sodium metal to form a higher alkane. 2 R−X + 2 Na → R−R + 2 NaX. The reaction is of little value except for intramolecular versions, such as 1,6-dibromohexane + 2 Na → cyclohexane + 2 NaBr.
The reaction begins with the formation of alkyl/arene-magnesium-halogen compound, followed by addition of proton source to form dehalogenated product. Egorov and his co-workers have reported dehalogenation of benzyl halides using atomic magnesium in 3P state at 600 °C. Toluene and bi-benzyls were produced as the product of the reaction. [9]