Rhodium complexes with dienes, arylation

Novel chiral diene ligands were reported to form highly active complexes with rhodium for asymmetric conjugate addition (236). Feng s ligand of a wedge structure provided a chiral environment around rhodium, giving excellent enan-tiocontrol in the asymmetric arylation of N-tosylarylimines (237) and in asymmetric 1,4-addition of aryl boronic acids (238). 

Several independent protocols using a combination of transition metal-catalyzed stereoselective hydrosilylation, such as palladium-catalyzed crosscoupling sequence leading to stereodefined r-conjugated alkene derivatives, have been successfully developed in the last decade (4). Alkenylsilanes or siloxanes, prepared via platinum or rhodium complex-catalyzed intermolecular hydrosilylation of terminal alkynes have been highly stereospecifically cross-coupled with aryl and alkenyl halides to give unsymmetrical stilbenes, alkenylbenzenes, and conjugated dienes (Scheme 24) (4). 

Rhodium Conjugate addition of aryl boronic acids to cyclohex-2-enone, catalysed by [Rh(diene)(OH)]2 complexes, afforded the corresponding product with the following enantioselectivities 96% ee with (508) ligand, 83% with (509), and 90% with (510). DFT calculations were used to shed light on the transition state structures and energies. " The sulfoxide-olefin ligand (511) exhibited >99% ee " ... 

Arylative cyclization of alkynals with arylboronic acids is catalyzed by rhodium-diene complexes and even proceeds enantioselectively in the presence of a chiral diene (Equation (48)).399... 

A variety of electrophiles are employed for carbonyl alkenylation and arylation that proceed through transmetalation from silicon to transition metal catalysts. For example, addition of alkenylsilanes and aryl(trimethoxy)si lanes to aldehydes is catalyzed by copper/DTBM-SEGPHOS, which mediates transmetalation from silicon to copper to give a wide variety of chiral alcohols with high degree of % ee (Scheme 3-144). The enantioselective alkenylation of imines using 2-(hydroxylmethyl)phenyl-substituted propen-2-ylsilane is catalyzed by a rhodium/chiral diene complex. ... 

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