676476-21-4Relevant articles and documents
A new modular phosphite-pyridine ligand library for asymmetric Pd-catalyzed allylic substitution reactions: A study of the key Pd-π-allyl intermediates
Mazuela, Javier,Pàmies, Oscar,Diéguez, Montserrat
, p. 2416 - 2432 (2013/04/23)
A library of phosphite-pyridine ligands L1-L12 a-g has been successfully applied for the first time in the Pd-catalyzed allylic substitution reactions of several di- and trisubstituted substrates by using a wide range of C, N and O nucleophiles, among which are the little studied α-substituted malonates, β-diketones, and alkyl alcohols. The highly modular nature of this ligand library enables the substituents/configuration at the ligand backbone, and the substituents/configurations at the biaryl phosphite moiety to be easily and systematically varied. We found that the introduction of an enantiopure biaryl phosphite moiety played an essential role in increasing the versatility of the Pd-catalytic systems. Enantioselectivities were therefore high for several hindered and unhindered di- and trisubstituted substrates by using a wide range of C, N and O nucleophiles. Of particular note were the high enantioselectivities (up to>99 % ee) and high activities obtained for the trisubstituted substrates S6 and S7, which compare favorably with the best that have been reported in the literature. We have also extended the use of these new catalytic systems in alternative environmentally friendly solvents such as propylene carbonate and ionic liquids. Studies on the Pd-π-allyl intermediates provide a deeper understanding of the effect of ligand parameters on the origin of enantioselectivity. A library of phosphite-pyridine ligands has been successfully applied in the Pd-catalyzed allylic substitution reactions of several di- and trisubstituted substrates by using a wide range of C, N, and O nucleophiles. By carefully selecting the ligand components, high regio- and enantioselectivities (up to >99 % ee) and good activities have been achieved (see scheme). The NMR studies on the Pd-π-allyl intermediates provide a deeper understanding of the effect of ligand parameters on the origin of enantioselectivity. Copyright
Chiral Pyridines: Optical Resolution of 1-(2-Pyridyl)- and 1-[6-(2,2′-Bipyridyl)]ethanols by Lipase-Catalyzed Enantioselective Acetylation
Uenishi, Jun'ichi,Hiraoka, Takao,Hata, Shinichiro,Nishiwaki, Kenji,Yonemitsu, Osamu,Nakamura, Kaoru,Tsukube, Hiroshi
, p. 2481 - 2487 (2007/10/03)
The resolution of racemic 1-(2-pyridyl)ethanols 2a-n, including the 2,2′-bipyridyl and isoquinolyl derivatives, by lipase-catalyzed asymmetric acetylation with vinyl acetate is reported. The reactions were carried out in diisopropyl ether at either room temperature or 60°C using Candida antarctica lipase (CAL) to give (R)-acetate and unreacted (S)-alcohol with excellent enantiomeric purities in good yields. The reaction rate was relatively slow at room temperature for substrates bearing an sp3-type carbon at the 6-position on the pyridine ring, such as 2c, 2d, and 2e, and for those bearing 1-hydroxypropyl and allyl groups at the 2-position on the pyridine ring, such as 21 and 2m. In such cases, a higher temperature was required. Thus, when the reaction was conducted at 60°C, it was accelerated 3- to 7-fold without losing the high enantiospecificity. However, the reaction of homoallylic alcohol 2n was not complete, even when the reaction was continued for a longer period of time at 60°C. This enzymatic resolution can be used practically in a wide range of reaction scales from 10 mg to 10 g or more. This catalyst can be used repeatedly with a 5-10% loss of the initial activity with each use.
