Vinyl halides metathesis

The presence of halogen atoms appears to exert little, if any, effect on catalyst activity, but it can influence the course of the metathesis reaction. Vinylic halides are unreactive, as exemplified by the ring-opening polymerization of l-chloro-l,5-cyclooctadiene, which afforded a perfectly alternating copolymer of butadiene and chloroprene (7/2) via polymerization exclusively through the unsubstituted double bond. 

A practical method for preparation of fluorinated alkenyl copper reagents has been recently developed from cuprous halides metathesis of the corresponding zinc or cadmium reagents [180]. These copper reagents exhibit excellent stability at room temperature and undergo a variety of coupling reactions with methyl, allyl, vinyl, aryl and acid halides [180] (Scheme 63). More recently, preparation of cyclic perfluoroalkenyl copper reagents has been reported by the same route [156-158]. 

Perfluoroalkynylcopper reagents can be prepared by metathesis reactions with the zinc or cadmium reagent (e.g., formation of 6) or by treatment of terminal (perfluoroalkyl)acetylenes with copper(I) chloride/ammonium hydroxide.69 Perfluoroalkynylcopper reagents react with aryl (e.g., formation of 7) and vinyl halides as well as undergoing oxidative dimerization reactions upon exposure to air.2... 

Similarly, Fischer carbene complexes are formed when Grubbs systems react with vinyl esters, vinyl carbonates, and vinyl halides. However, these Fischer car-benes are known to decompose to give terminal ruthenium carbide species by elimination of HX (X = OjCR, OjCOR, halide) [83-86]. Notably, the formation of the carbide complexes is less favorable in phosphine-free systems, which enables the Hoveyda [56] and Piers [87] catalysts to promote the cross metathesis of vinyl hahdes and terminal or internal olefins [88]. 

The metathesis of vinyl halides is possible but does not always proceed smoothly due to the potential for the formation of by-products from the intermediate carbene species. Vinyl chloride substrates that have been known to undergo metathesis smoothly, include an intermediate from Stoltz s synthesis of Elatol (see Scheme 2.16), but in this case the formation of a vinyl... 

Macnaughtan ML, Johnson MJA, KampfJW. Olefin Metathesis Reactions with Vinyl Halides Formation, Observation, Interception, and Fate of the Ruthenium-Monohalomethylidene Moiety.JHm Chem Soc. 2007 129(25) 7708-7709. 

Some alkenes with heteroatoms can be used in cross-coupling reactions. Vinyl boranes are an important group, as the carbon-boron bond can subsequently be converted into so many other functional groups, such as halides (Scheme 8.97). ° An example of cross-metathesis of a vinyl borane, followed by Suzuki coupling, can be found in Scheme 11.40. An example of a vinyl silane metathesis can be found in Scheme 2.110. 

Allylsilanes can be prepared by a wide array of methods, including (1) the reaction of allyl metals with ClSiRs, (2) the reaction of silylanions (MSiRs) with allylic substrates, (3) the Kumada coupling of Me3SiCH2MgBr with vinyl halides, catalyzed by Pd or Ni species, (4) the Wittig reaction of P-silylated Wittig reagents, (5) the cross-metathesis of olefins with allylsilanes, and (6) the reductive silylation of unsaturated compounds. ... 

Morrill C, Grubbs RH. Synthesis of functionalized vinyl bor-onates via ruthenium-catalyzed olefin cross-metathesis and subsequent conversion to vinyl halides. J. Org. Chem. 2003 68 6031-6034. 

Since the early disclosure by Negishi that zinc halide salts accelerate Pd(0) -catalyzed crosscouplings between vinyl zirconocenes and various halides [78], several methods have been developed that extend the utility of this metathesis process from a zirconium chloride to a zinc chloride (79 Scheme 4.47). Alternatively, routes to more reactive diorganozinc intermediates, e. g., using Me2Zn, convert readily available zinc derivatives to mixed species 80, which selectively couple with various electrophiles [14]. 

Tetrafluoropyridyl organometallic reagents can be prepared by reaction of 4-bromotetra-fluoro- or tctrafluoro-4-iodopyridine with zinc or cadmium in dimethylformamide at room temperature.83 Metathesis of these reagents with copper(l) bromide affords the (2.3,5,6-tetra-fluoro-4-pyridyl)copper reagent. The latter species undergoes high-yield substitution reactions with allyl halides, vinyl iodides, aryl iodides, and alkanoyl halides. 

This reaction has been modified for various conditions, such as the application of microwave irradiation and the application of phosphine-containing polymer prepared from the ruthenium-catalyzed ring-opening metathesis polymerization of the norbornene. Most importantly, this reaction has been extended to the coupling of primary or secondary alkyl halides with aryl, vinyl, and even alkyl halide (or tosylate) 31,3o,3p,3y,3dd,3nn,4v,4x,6... 

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