Tridentate carbazole ligands

Suzuki, T., Kinoshita, A., Kawada, H., Nakada, M. A new asymmetric tridentate carbazole ligand Its preparation and application to Nozaki-Hiyama allylation. Synlett 2003, 570-572. 

In an extension to this work, a similar tridentate carbazole ligand 15a was prepared resulting in an electronically and sterically different environment for the binding of chromium. This modified ligand provided superior enantioselectivities in a range of NHK processes (Scheme 12.14). ... 

Inoue, M., Suzuki, T., Nakada, M. Asymmetric Catalysis of Nozaki-Hiyama Allylation and Methallylation with A New Tridentate Bis(oxazolinyl)carbazole Ligand. J. Am. Chem. Soc. 2003,125, 1140-1141. 

Nakada et al. developed a tridentate C2-symmetric bis (oxazolinyl)carbazole ligand 15 and proposed that this tridentate ligand would provide enhanced enantioselectivities as a result of stabilization of the allyl-Cr(lll)-ligand complex because of the presence of a o-bond with the carbazole nitrogen and two coordination bonds to the oxazoline nitrogens, which leaves a vacant coordination site at which an aldehyde can bind. ... 

SCHEME 12.13. Application of Nakada et al. s tridentate C2-symmetric bis(oxazolinyl)carbazole ligand 15. 

Nakada et al. applied the tridentate carbazole-derived ligand 15a in the methallylation of chiral aldehyde 50 to give 51, which is a key intermediate of calcitriol lactones. Ligand 15a gave 51 in 94% de (Scheme 12.37), whereas... 

Inoue M, Suzuki T, Kinoshita A, Nakada M. Catalytic asymmetric Nozaki-Hiyama-Kishi reactions with a tridentate bis (oxazolinyl)carbazole ligand. Chem. Rev. 2008 108 169-181. 

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