Effects of Ligands and Additive Alcohols on Enantioselection in Highly Efficient Asymmetric Borohydride Reduction of Ketones Catalyzed by Optically Active Aldiminato Cobalt(II) Complexes

Nagata, Takashi; Sugi, Kiyoaki D.; Yamada, Tohru; Mukaiyama, Teruaki

doi:10.1055/s-1996-5693

Cited by 23 publications

(14 citation statements)

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“…Fast reaction was realized, and the chemical yield and the enantioselectivity were rather improved compared with those from the corresponding batch system. For an acyclic ketone or a steric demanding ketone, the enantioselectivities in the batch system 16 were reproduced in the continuous-flow system (entries 5 and 6). Reaction heat generated in the batch system might lead to overreaction due to manual handling of syringes and less efficient heat transfer than that in the flow system.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Homogeneous Enantioselective Catalysis in a Continuous-Flow Microreactor: Highly Enantioselective Borohydride Reduction of Ketones Catalyzed by Optically Active Cobalt Complexes

Hayashi

Kikuchi

Asano

et al. 2012

Org. Process Res. Dev.

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Highly enantioselective homogeneous catalysis under continuous-flow conditions was established for the cobalt-catalyzed borohydride reduction of tetralone derivatives. A microreactor allowed higher reaction temperature with the residence time of 12 min than the corresponding batch system to maintain enantioselectivity as well as reactivity. The present system was directly applied to gram-scale synthesis to afford the reduced product with 92% ee.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Homogeneous Enantioselective Catalysis in a Continuous-Flow Microreactor: Highly Enantioselective Borohydride Reduction of Ketones Catalyzed by Optically Active Cobalt Complexes

Hayashi

Kikuchi

Asano

et al. 2012

Org. Process Res. Dev.

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“…The search for economical methods of enantioselective reduction of ketones to secondary alcohols is a rewarding goal, owing to the numerous applications in the fields of pharmaceuticals, agrochemicals, and flavor and fragrance . Known industrial methods involve reduction by chiral hydride reagents such as Corey's oxazaborolidine, Yamaguchi−Mosher reagent LiAlH 4 coordinated by BINAL-H or Chirald, Mukaiyama's reduction of ketones by NaBH 4 in the presence of chiral Co(II) complexes, or Brown's chiral boranes such as Alpine-Borane 9a-d or chiral amino alcohols.…”

Section: Introductionmentioning

confidence: 99%

Enantioselective Reduction of Ketones by Polymethylhydrosiloxane in the Presence of Chiral Zinc Catalysts

et al. 1999

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Enantioselective reduction of ketones, particularly acetophenones, by polymethylhydrosiloxane (PMHS) to the corresponding secondary alcohols can be achieved with high yields and enantiomeric excesses (ee's) up to 88% in the presence of chiral zinc catalysts (eq 1). Two catalytic systems have been developed giving similar ee's: (i) System A: ZnEt2 + chiral diimine or diamine 1 − 10. (ii) System B: Zn(carboxylate)2 + chiral diamine activated by Vitride. System B is inexpensive, stable, and ready to use in toluene, providing either (R) or (S) chiral secondary alcohols with 70−80% ee in the presence of (S,S)- or (R,R)-N,N‘-ethylenebis(1-phenylethylamine) (ebpe, 6). The reduction has been carried out at the 1 kg scale without scale-up problems. The ligand is cheap and is recovered at the end of reaction by simple distillation from residues of the organic phase. Both precursors ZnMe2·(S,S)-ebpe (A) and Zn(dea)2·(S,S)-ebpe (B) for systems A and B, respectively, have been isolated and characterized by X-ray structure and exhibit the same catalytic properties and the same ee's for the reduction of acetophenone as the in situ prepared catalytic system. The complex ZnEt2·(S,S)-ebpe) (A‘) reacts with benzaldehyde to give the seven-membered ring dimer complex La in which benzaldehyde inserts into the Zn−N bond of complex A‘. Acetophenone also reacts with A‘ to give a similar seven-membered ring dimer complex Lb. Both La and Lb are catalysts for the enantioselective reduction of acetophenone by PMHS and gave activities and ee's similar to those of A‘. Synthetic and mechanistic aspects of this new economical method are discussed in this paper.

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“…In the presence of the tetrahydrofurfuryl alcohol, a higher enantioselectivity as well as a faster reaction rate were realized [42]. It is noted that a suitable cobalt(II) complex catalyst should be chosen corresponding to the substrates to achieve high enantiomeric excesses [43]. More than several hundred TONs were achieved and some of the efficient cobalt(II) complex catalysts are now available commercially [44].…”

Section: Enantioselective Borohydride Reductionmentioning

confidence: 99%

Manganese and cobalt 3-oxobutylideneaminato complexes: Design and application for enantioselective reactions

Yamada

Ikeno

Ohtsuka

et al. 2006

Science and Technology of Advanced Materials

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The optically active 3-oxobutylideneaminato transition-metal complexes have been developed as efficient catalysts for a variety of enantioselective reactions; e.g. the corresponding manganese(III) complexes catalyzed the enantioselective aerobic epoxidation of unfunctionalized olefins, and the corresponding cobalt complexes have been developed for the enantioselective borohydride reduction of various carbonyl compounds. The cobalt complexes could also be employed for the catalytic enantioselective cyclopropanation with diazoacetates and the Lewis acid catalyses such as the hetero Diels-Alder reaction, carbonyl-ene reaction, and 1,3-dipolar cycloaddition of nitrones. In the presence of the cobalt complex, the Henry reaction proceeded with a high enantioselectivity, and the enantioselective chemical fixation of carbon dioxide to obtain the optically active cyclic carbonate. In these Lewis acid catalyses, the valence of cobalt and the counter anion have significant effects on the reaction rate and stereoselectivity. q

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Effects of Ligands and Additive Alcohols on Enantioselection in Highly Efficient Asymmetric Borohydride Reduction of Ketones Catalyzed by Optically Active Aldiminato Cobalt(II) Complexes

Cited by 23 publications

References 0 publications

Homogeneous Enantioselective Catalysis in a Continuous-Flow Microreactor: Highly Enantioselective Borohydride Reduction of Ketones Catalyzed by Optically Active Cobalt Complexes

Homogeneous Enantioselective Catalysis in a Continuous-Flow Microreactor: Highly Enantioselective Borohydride Reduction of Ketones Catalyzed by Optically Active Cobalt Complexes

Enantioselective Reduction of Ketones by Polymethylhydrosiloxane in the Presence of Chiral Zinc Catalysts

Manganese and cobalt 3-oxobutylideneaminato complexes: Design and application for enantioselective reactions

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