Coupling, organometallic

This organometallic coupling reaction is useful in organic synthesis because it forms carbon-carbon bonds, thereby making possible the preparation of larger molecules from smaller ones. As the following examples indicate, the coupling reaction can be carried out on aryl and vinylic halides as well as on alkyl halides. 

In some examples it is not necessary to prepare the organometallic-coupling agent R2MX2 beforehand. Thus coating glass fibres with a heptane or alcohol solution of titanium alkoxide promotes adhesion between the fibre and polymer, e.g., acrylic, polyolefins, polyester, polyamide and other thermoplastic resins. 

Vinylphosphates are converted into dienes by reduction or organometallic coupling, respectively, and into the corresponding iodides by treatment with TMSCl/Nal in MeCN.38... 

Carbon-carbon bond formation is fundamental to all of organic chemistry. Nucleophilic displacement is still the basis for most of what we do, but over the past thirty years radical addition and organometallic coupling have both been brought to a level of practical importance. 

In a useful extension to this chemistry, the coupling of the starting iodoaniline with trimethylsilylalkynes was found to give the silylated species 5, which can bp a useful precursor to either 2-unsubstituted indoles or 2-halogenated derivatives as shown in Scheme 8. These could then be taken on further with standard organometallic coupling reactions. 

In conclusion, for the most part, polymers incorporating phosphole units are still rare. However, the work described above demonstrates that they are accessible via a number of diverse synthetic routes including organometallic coupling or electropolymerization processes. The general property-structure relationships established with well-defined small oligomers have been shown to extend to the corresponding polymeric materials. 

It has proven possible to couple alkynyl iodides and bromides with a wide variety of zinc cyanocuprates. Coupling tolerates a number of functional groups on both the alkyne and the cuprate, including alkynyl ethers and propargyl ethers (equations 46 and 47). The cuprate partners have been primary alkyl, vinyl and aryl based59-61, whereas secondary alkyl organometallics couple in some cases and reduce the alkynyl halide in others. 

Organometallic coupling reactions are useful for forming large molecules from small pieces. 

In summary, the development in the field of total syntheses of the antitumor agent camptothecin nicely illustrates the progress of modern synthesis over the last decade. Radical reactions and organometallic coupling reactions, for example, have reached such a level of maturity that they now belong to the standard repertoire of key steps in the construction of complex molecules. 

Another, mechanistically closely related reaction is the cross-coupling reaction of aryl, benzyl, vinyl, or allyl halides with organometallic coupling reactions, such as Grignard reagents or, preferably, less reducing organometallics such as tin compounds or boronic acids RB(OH)2 the latter allow the reaction to be conducted even in aqueous media.83 The principal reaction steps are ... 

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