Functional group transformation, chiral metal

Fragrances, giant-scale synthesis, 9, 95, 102 Frontier molecular orbitals, 213 Functional group transformation, chiral metal complexes, 225... 

Enzyme-mediated oxidation reactions offer highly diverse options for the modification of existing functional groups as well as for the introduction of novel function in chiral catalysis. Biooxidations often enable us to obtain complementary solutions to metal-assisted transformations and organocatalysis and are considered one of the important strategies of green chemistry . 

Boronic esters have been used in a wide range of transformations. These useful reagents have been transformed into numerous functional groups and are essential reagents for several C-C bond-forming reactions. Transition metal-catalyzed hydroboration of olefins often leads to mixtures of branched and linear products. Several groups have reported asymmetric reductions of vinyl boronic esters [50-52] with chiral rhodium P,P complexes however, the first iridium-catalyzed reduction was reported by Paptchikhine et al (Scheme 10) [53]. 

Trimethylsilyloxyfuran reacted stereoselectively with chiral tungsten carbene complexes in a Mukaiyama-Michael addition fashion to provide -products, as shown in Equation (18) <2005AGE6583>. The metal carbene in the butenolide product serves as a useful functional group for further transformations. 

It is worth mentioning that BNP anions without a metal counterpart, were used as powerful organocatalysts to carry out a variety of asymmetric reactions such as epoxydation of enals reported by List et al The related chiral phosphoric acids HBNP, with bulky functional groups at the 3, 3 positions, are also powerful catalysts. Pioneered by Akiyama et al. and Terada and coworkers, they have recently been applied to a wide range of asymmetric organic transformations.However, this area will not be discussed here since it is beyond the scope of this chapter but the reader may consult the cited references. 

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