Metathesis chemistry chiral catalysts

So what is left to be accomplished During the current decade one can expect further asymmetric applications and catalyst designs for metathesis reactions, a maturing of chiral catalyst development for cyclopropanation and insertion with increasing synthetic applications, and decreased reliance on traditional Fischer carbenes in synthesis. Major changes remain for ylide applications, especially those that can be enantioselective, in catalytic carbene chemistry, and advances in nitrene chemistry that are comparable to those achieved over the years in carbene chemistry are in their infancy. 

Although the Heck reaction mainly involves the formation of bonds between sp -hybridized carbon atoms, there are asymmetric versions. One approach is to capture the chirality of the insertion intermediate by ensuring the p-hydride elimination either occurs away from the site of the original alkene (Scheme 5.35), or is pre-empted by a different step such as another insertion in a tandem process. Another approach is to provide a symmetrical substrate with two enantiotopic alkenes (Scheme 5.36), an approach also used in metathesis chemistry (Section 8.3.6). In all of these reactions, the source of chirality is from the employment of chiral ligands for the palladium catalyst, often chelating bisphosphines. 

Perhaps the most compelling research objective in this area will involve the development of a chiral metathesis catalyst that effects C-C bond formation efficiently and with excellent levels of enantioselectivity [41 ]. In such a case, all the reactions discussed herein, in addition to those expertly developed in other laboratories [40], will become subject to asymmetric catalysis. Such a development should prove to have an enormous impact on the field of inorganic, organome-tallic and synthetic organic chemistry. 

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