139199-71-6Relevant articles and documents
Novel C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands: Synthesis and application in asymmetric diethylzinc addition to aldehydes
Shih, Yi-Shan,Boobalan, Ramalingam,Chen, Chinpiao,Lee, Gene-Hsian
, p. 327 - 333 (2014/04/03)
First synthesis of C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands is described. The Mukaiyama-Michael reaction was applied as an important reaction for the synthesis of 2,2-bipyridylpropane 9. Among the ligands synthesized, ligand 11 exhibits excellent chiral induction (up to 97% ee) in diethylzinc addition to various aldehydes. The use of additional Lewis acid such as Ti(OiPr)4 in diethylzinc addition reaction is not required for the present catalytic system.
Ti-TADDOLate-Catalyzed, Highly Enantioselective Addition of Alkyl- and Aryl-Titanium Derivatives to Aldehydes
Weber, Beat,Seebach, Dieter
, p. 7473 - 7484 (2007/10/02)
Toluene-ether or toluene-hexane solutions of aryl and alkyl triisopropoxy titanium reagents (free of Li, Mg, or Zn salts) are prepared from the corresponding Li or Grignard reagents and ClTi(OiPr)3, with careful removal of salts (centrifugation of LiCl or of dioxane*MgX2, and addition of 12-crown-4).The solutions of the organotitanium compounds are combined with one equiv. of an aldehyde and 0.2 equiv. of (R,R)-diisopropoxy-(α,α,α',α'-tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethanolato) titanium (Ti-TADDOLate 3) at dry-ice temperature.Warming up to room temperature leads to nucleophilic addition to the (Si)-face of the aldehydes with enantioselectivities as high as 99.5 : 0.5 (products 4-33 in Scheme 4).Functional groups or protecting groups and branching in the Ti-R group and in the aldehyde must be remote from the reacting centers.Aryl groups can be added to aldehydes by this method. - In contrast to all the enantioselective R2Zn additions to aldehydes, in which only one R-group is actually transferred, a twice as economic use is made of the originally employed R-metal reagent in the method described here. - A procedure for multigram preparation of the spiro-Ti-TADDOLate (2) employed for the in situ generation of catalyst (3) is described, and details of the determination of enantiomer ratios (er) by GC and NMR methods are given (Tab. 2, 3).The mechanistic interpretation of Ti-TADDOLate-mediated nucleophilic additions as derived previously (ref.4c) is also compatible with this monometallic variant of the method.
