Functional group transformation, chiral metal complexes

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

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. 

Shibasaki pioneered the use of chiral heterobimetallic complexes of BINOL as catalysts for an impressively wide variety of useful asymmetric transformations (Schemes 12.15 and 12.16) [116-119]. The complexes, typically consisting of a group 3 or a group 13 metal ion in combination with alkali metal ions, have been suggested to exhibit dual function as Lewis acids and Bronsted bases. Such complexes are generated in situ upon mixing of BINOL with metal salts in the appropriate proportions and consequently represent a notable example of macromolecular self-assembly. 

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