Titanium 3,3′-Modified-Biphenolate Complexes Atropisomerically Controlled by TADDOLs: Novel Chiral Lewis Acid Catalysts for Asymmetric Methylation with an Achiral Methyl-Titanium Reagent
作者:Makoto Ueki、Yosuke Matsumoto、Jonathan J. Jodry、Koichi Mikami
DOI:10.1055/s-2001-18770
日期:——
Chiral Ti complexes, which are constituted of 3,3′-modified-biphenolate (BIPOLate) ligands atropisomerically controlled by (R)-TADDOLs, are shown to be novel chiral Lewis acid catalysts for the methylation reaction of aldehydes with an achiral methyl-titanium reagent. Thus, the chiral 3,3′-modified BIPOLate/TADDOLate-Ti complexes give enhanced enantioselectivities up to 100% enantiomeric excess.
Conformationally Driven Asymmetric Induction of a Catalytic Dendrimer
作者:Jianfeng Yu、T. V. RajanBabu、Jon R. Parquette
DOI:10.1021/ja802308a
日期:2008.6.1
Nature's catalysts promote the reactions necessary for life with extremely high specificity by folding into specific shapes capable of communicating remote structural information to an active site. Achieving this objective in synthetic systems has been hampered by the lack of information concerning how dynamic conformational chirality can influence the stereoselectivity of a catalytic process. Herein, we report the first illustration of a catalytic dendrimer that achieves high enantioselectivity by amplifying/propagating local chirality via a dynamically folded structure. Experimental evidence supports a chiral relay mechanism that propagates local terminal chirality of the dendron to the axial chirality of the biphenyl core through the helical secondary structure of the dendron.