Atsuhiro Ookawa

Bio: Atsuhiro Ookawa is an academic researcher from University of Tokyo. The author has contributed to research in topics: Sodium borohydride & Enantioselective synthesis. The author has an hindex of 11, co-authored 26 publications receiving 711 citations.

Mixed solvents containing methanol as useful reaction media for unique chemoselective reductions within lithium borohydride

Abstract: Etude de la reduction d'esters, de lactones d'epoxydes par le systeme tetrahydroborate de lithium-methanol-diethylether. Reduction de carboxamides par LiBH 4 -methanol-diglyme (ou THF)

Complementary catalytic asymmetric induction in the enantioselective addition of diethylzinc to aldehydes

Abstract: Both enantiomers of sec-alcohols were obtained in high enantiomeric excess (up to 92%) from the enantioselective addition of diethylzinc to aldehydes using chiral pyrrolidinylmethanol derivatives as catalysts.

Reduction of Azides to Amines with Sodium Borohydride in Tetrahydrofuran with Dropwise Addition of Methanol

Abstract: Obtention en particulier d'octylamine, anilines, naphtyl-1 amine, benzylamine, et de p-toluenesulfonamide par reduction des azides correspondants

Catalytic enantioselective addition to imines.

Abstract: Chiral nitrogen-containing compounds are widely distributed in nature and include many biologically important molecules (Chart 1). In these compounds, the nitrogen-containing units are known to play important roles for their bioactivities. For the synthesis of these chiral nitrogen-containing building blocks, use of imines as electrophiles is the most promising and convenient route.1 While many approaches using chiral imines or chiral nucleophiles have been reported,1 these diastereoselective reactions have some disadvantages. First, the procedures to introduce chiral auxiliaries to substrates and to remove them after the diastereoselective reactions are often tedious. Second, more than stoichiometric amounts of chiral sources are needed to obtain chiral compounds according to these reactions. On the other hand, catalytic enantioselective reactions provide the most efficient methods for the synthesis of chiral compounds,2 because large quantities of chiral compounds are expected to be prepared using small amounts of chiral sources. While much progress has been made recently in catalytic enantioselective reactions of aldehydes and ketones such as aldol,3 allylation,4 Diels-Alder,5 cyanation reactions,6 reduction,1b,2b etc., progress in catalytic enantioselective reactions of imines is rather slow. There are some difficulties in performing catalytic enantioselective reactions of imines. For example, in the cases of chiral Lewis acid promoted asymmetric Shū Kobayashi was born in 1959 in Tokyo, Japan. He studied chemistry at the University of Tokyo and received his Ph.D. in 1988 (Professor T. Mukaiyama). After spending 11 years at Science University of Tokyo (SUT), he moved to Graduate School of Pharmaceutical Sciences, University of Tokyo, in 1998. His research interests include development of new synthetic methods, development of novel catalysts (especially chiral catalysts), organic synthesis in water, solid-phase organic synthesis, total synthesis of biologically interesting compounds, and organometallic chemistry. He received the first Springer Award in Organometallic Chemistry in 1997.

Catalytic Asymmetric Organozinc Additions to Carbonyl Compounds

Abstract: Because of the tremendous effort of a great number of researchers, the catalytic asymmetric dialkylzinc addition to aldehydes has become a mature method. Ligands of diverse structures have been obtained, and high enantioselectivity for all different types of aldehydes have been achieved. Among the representative excellent catalysts are compounds 1, 8, 120, 325, 352, and 360 discussed above. However, compared to the well-developed dialkylzinc addition, the catalytic asymmetric reactions of aryl-, vinyl-, and alkynylzinc reagents with aldehydes are still very much under developed. Although catalysts such as (S)-402 and 210 prepared by Pu and Bolm have shown good enantioselectivity for the reaction of diphenylzinc with certain aromatic and aliphatic aldehydes, the generality of these catalysts for other [formula: see text] arylzinc reagents have not been studied. The vinylzinc additions using ligands 1 and 412 reported by Oppolzer and Wipf were highly enantioselective for certain aromatic aldehydes but not as good for aliphatic aldehydes. Carreira discovered highly enantioselective alkynylzinc additions to aldehydes promoted by the chiral amino alcohol 415, but this process was not catalytic yet. Ishizaki achieved good enantioselectivity for the catalytic alkynylzinc addition to certain aldehydes by using compounds 160, but the enantioselectivity for simple linear aliphatic aldehydes was low. Another much less explored area is the organozinc addition to ketones. Yus and Fu showed very promising results by using ligands 381 and 406 for both dialkylzinc and diphenylzinc additions to ketones, but the scope of these reactions were still very limited. Therefore, more work is needed for the aryl-, vinyl-, and alkynylzinc additions and for the organozinc addition to ketones, although many good catalysts have been obtained for the dialkylzinc addition to aldehydes. Development of these reactions will allow the catalytic asymmetric synthesis of a great variety of functional chiral alcohols that are either the structural units or synthons of many important organic molecules as well as molecules of biological functions. Macromolecular chiral catalysts have become a very attractive research subject in recent years because these materials offer the advantages of simplified product isolation, easy recovery of the generally quite expensive chiral catalysts, and potential use for continuous production. Three types of macromolecules including flexible achiral polymers anchored with chiral catalysts, rigid and sterically regular main chain chiral polymers, and chiral dendrimers have been used for the asymmetric organozinc addition to aldehydes. Among these materials, the binaphthyl-based polymers such as (R)-451 developed by Pu have shown very high and general enantioselectivity. Study of the binaphthyl polymers in the asymmetric organozinc addition has demonstrated that it is possible to systematically modify the structure and function of the rigid and sterically regular polymer for the development of highly enantioselective polymer catalysts. The catalytic properties of highly enantioselective monomer catalysts can also be preserved in the rigid and sterically regular polymer provided the catalytically active species of the monomer catalyst is not its aggregate. The TADDOL-based polymers and dendrimers prepared by Seebach showed very high and stable enantioselectivity for the diethylzinc addition to benzaldehyde even after many cycles. These studies on macromolecular chiral catalysts demonstrate that these materials are potentially very useful for practical applications.

Perspectives in catalytic applications of mesostructured materials

Abstract: This review paper deals with proven and potential applications of mesoporous molecular sieves in catalysis. In addition to introduction and conclusion, the text is divided into two parts, respectively, dedicated to the design of solid catalysts and catalyst supports and to some relevant examples of catalytic processes.

Enantioselective Automultiplication of Chiral Molecules by Asymmetric Autocatalysis

Abstract: Asymmetric autocatalysis is a process of automultiplication of a chiral compound in which chiral product acts as a chiral catalyst for its own production. The discovery and the development of asymmetric autocatalysis of pyrimidyl-, quinolyl-, and pyridylalkanols are described in the enantioselective additions of diisopropylzinc to the corresponding nitrogen-containing aldehydes. (Alkynylpyrimidyl)alkanols automultiply with a yield of over 99% and over 99.5% ee. Asymmetric autocatalysts with extremely low ee's automultiply with significant amplification of ee's without the need for any other chiral auxiliaries. Small enantiomeric imbalances of chiral molecules induced by physical factors can be amplified by the present asymmetric autocatalysis.