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2,2’-dihydroksy-1,1’-binaftyl (BINOL) i jego pochodne. Wybrane syntezy i zastosowanie. Część. II

Krasowska D.

Wiadomości Chemiczne

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2013

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[Z] 67, 1-2

55--92

EN

An invention of new catalytic strategies for stereoselective synthesis is of current interest to many laboratories worldwide . Over the past few decades a remark - able progress in the field of stereocontrolled synthesis has been achieved with chiral 1,1’-binaphthyl compounds. Optically active 1,1’-binaphthyl-2,2’-diol (BINOL) and its derivatives due to their axial dissymmetry and molecular flexibility have been widely utilized as chiral ligands and auxiliaries in stoichiometric or catalytic asymmetric reactions, such as metal-catalysed transformations and enantioselective organocatalysis. BINOL and its functionalized analogues have demonstrated remark - able chiral discrimination properties. Extensive studies on molecular recognition provided the successful results in the application of BINOL as a host for an optical resolution of racemic guests and as a chiral NMR shift reagent for the determination of chiral compounds. It has been found that the axial chirality of binaphthyl units in host molecules is crucial contribution to their stereoselctive complexation with chiral guests.

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Asymetryczne przeniesienie wodoru do ketonów katalizowane związkami Rutenu(II) i Rodu(III)

Karczmarska-Wódzka A., Kołodziejska R., Studzińska R., Wróblewski M.

Wiadomości Chemiczne

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2012

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[Z] 66, 3-4

273-295

EN

Asymmetric hydrogen transfer (ATH) is one of the methods of stereoselective reduction of prochiral carbonyl compounds (Scheme 6). Complexes of the platinum group metals (Noyori catalysts) are the most common catalysts for AT H reactions. The specific structure of the Noyori catalyst allows to activate two hydrogen atoms. These atoms are transferred from donor to acceptor in the form of hydride ion and proton (Scheme 1). Depending on the used catalyst the transfer hydrogenation of ketons can proceed by direct and indirect transfer mechanism. The direct hydride transfer from a donor to an acceptor proceeds via a six-membered transition state (3) (Scheme 2). The indirect hydride transfer proceeds through the formation of an intermediate metal hydride. A monohydride (HLnMH) and or a dihydride (LnMH2) can be formed depending on the catalyst that is used (Scheme 3). In the monohydride route, the reduction proceeds in the inner sphere of the metal (four-membered transition state (4)) or in the outer sphere of the metal (six-membered transition state (5)) (Scheme 4). The proposed reduction of carbonyl compounds in the AT H reaction by Noyori catalysts uses the mechanism of the hydride ion and proton transfer from the donor to the catalyst and the formation of the monohydride. In the indirect transfer hydrogenation the hydride ion and proton are transferred from the monohydride to the acceptor (Scheme 5, 7). AT H reactions that lead to chiral alcohols are conducted in organic solvents or in water. Hydrogen donors most often used in organic solvent reactions are propan-2-ol or an azeotropic mixture of formic acid and triethylamine (Tab. 1, 6). Sodium formate is usually used as hydrogen donor in the reactions conducted in water. Yield and enantioselectivity of the reaction depend on many factors the most important of which are: the structure of a substrate, hydrogen donor and solvent that were used, the reaction time, substrate concentration, and the S/C ratio [2]. In the case of asymmetric reduction conducted in water the solvent pH is also of great importance [3, 7, 8]. An optimal pH range depends on the type of a catalyst [7, 8]. AT H reactions conducted in water are distinguished by a shorter reaction time and higher enantioselectivity than the reactions conducted in organic solvents. In addition, catalysts used in the AT H reactions are more stable in water allowing reuse of the catalyst without loss of its activity. This paper presented examples of the use of specific catalysts in asymmetric reactions of hydrogen transfer. In particular, I drew attention to the reactions running in the aquatic environment due to the above-mentioned advantages of this solvent. The authors focused specifically on bifunctional catalysts based on Ru(II) and Rh(III) on the account of wide usage of the catalysts of that type in AT H reactions in water and their good performance [8, 9, 15, 16, 17, 19, 20, 21, 22]. p-Cymene is the most common aromatic ligand in catalysts based on Ru(II) while in the case of catalysts with Rh(III) the most common is anionic pentamethylcyclopentadienyl ligand. In both cases the second most common ligands are diamines or amino alcohols (Scheme 8). There are better performance and enantioselectivity when diamines are used as ligands. Attempts to replace diamines and amino alcohols by Schiff bases (Scheme 13) in the catalysts containing Rh(III) proved poor results due to a very low enantioselectivity of conducted reactions (Tab. 7).

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2,2'- Dihydroksy-1,1'-binaftyl (BINOL ) i jego pochodne. Wybrane syntezy i zastosowanie. Część I

Krasowska D.

Wiadomości Chemiczne

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2012

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[Z] 66, 5-6

485-528

EN

1,1’-Binaphthyl and its derivatives represent a particular class of chemical molecules which chirality results from the restricted rotation about single bond of the two naphthalene rings. This generates the chirality axis. Therefore 1,1’-binaphthyl derivatives exist as two enantiomeric forms called atropoisomers. Moreover, 1,1’- binaphthyls with substituents at 2,2’ position exhibit higher rotational barriers around the 1,1’-axis, which affect a very stable chiral configuration. The classical examples of such molecules is 2,2-dihydroxy-1,1’-binaphthyl (BINOL ), which has become one of the most utilized chiral ligand and auxiliary for diverse asymmetric syntheses. The unchallenged success of BINOL and its derivatives in the field of transition metal-catalyzed asymmetric reactions or C-C bond forming reactions promoted worldwide an advancement of organic synthesis. The first synthesis of BINOL as racemate was described in 1873. Since then there have been found numerous efficient methods of racemic or enantiomerically pure BINOL preparation and its derivatization. In order to present a brief overview of the most convenient and facile routes to obtain racemic and nonracemic symmetrically substituted 1,1’-binaphthyls based on stoichiometric and catalytic oxidative coupling, classical optical resolution, kinetic enzymatic resolution of racemic mixture or regioselective modification of the binaphthol scaffold the following article is presented.