An alkenyl halide is a compound whose molecule has one or more halogen atoms bonded to an alkenyl group. Alkenyl halides are a class of unsaturated halocarbons that can be categorized into the following two classes: 1. Alkenyl halides whose halogen atoms are directly attached to carbon atoms in a carbon-carbon double bond such as vinyl chloride. 2. Alkenyl halides with halogen attached to a carbon atom, such as allyl bromide and 3-chlorocyclohexene.
Applications
Cross-coupling reaction: Palladium-catalyzed cross-coupling reactions involving alkenyl halides are the origin of several of the most commonly used reactions. It has been reported that C-C bond formation occurs smoothly in water at room temperature by simply combining an aryl bromide with an alkyl iodide in the presence of zinc powder and a palladium catalyst. At the same time, this method provides a high level of maintenance of the E- and Z-olefin geometry in the zinc-mediated reactions, which is more favorable compared to the traditional two-step Negishi cross-coupling reaction in ether media. It is noteworthy that it is easy to undergo the cross-coupling with asymmetric 2,2-disubstituted alkenyl halides under these conditions with complete retention of configuration. Both primary and secondary alkyl halides react, although use of alkyl bromides is preferred for more sterically hindered disubstituted alkenyl halides. In the latter case, alkyl iodides are easily consumed.
Carbonyl addition: The reaction of alkenylmetal reagents such as alkenyl lithium, alkenyl magnesium, or alkenyl copper with carbonyl compounds is useful for the synthesis of allylic alcohols. Alkenyl chromium compounds are readily derived from alkenyl halides and anhydrous chromium chloride in N,N-dimethylformamide(DMF) and that the organometals add selectively to aldehydes to produce allylic alcohols. And the simple operation of the procedure is illustrated for the synthesis of 2-methyl-1-phenyl-2-propen-l-ol.
Mechanistic probe: It has been suggested that many reaction traditionally classed may proceed via single electron transfer (SET) processes. The results of experiments with rearrangeable alkenyl halide probes have often been cited as evidence to support the conclusion that an SET mechanism is operative. Reactions which interfere with the standard analysis include the rearrangement of nonradical intermediates and the isomerization of the starting probe halide by a halogen atom transfer mechanism.
Reference
- Krasovskiy A, Duplais C, Lipshutz B H. Stereoselective Negishi-like couplings between alkenyl and alkyl halides in water at room temperature[J]. Organic letters, 2010, 12(21): 4742-4744.
