Mechanism of the Asymmetric Dehydrative Allylative Cyclization of Alcohols to Cyclic Ethers Catalyzed by a CpRu Complex of the Chiral Picolinic Acid-Type Ligand, Cl-Naph-PyCOOH: Is a π-Allyl Intermediate Present?

• Yusuke Suzuki

  Graduate School of Pharmaceutical Sciences, Nagoya University, Chikusa, Nagoya, Aichi 464-8601 , Japan

• Shoutaro Iwase

  Graduate School of Pharmaceutical Sciences, Nagoya University, Chikusa, Nagoya, Aichi 464-8601 , Japan

• Manussada Ratanasak

  Institute for Catalysis, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, Hokkaido 001-0021 , Japan

• Jun-ya Hasegawa

  Institute for Catalysis, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, Hokkaido 001-0021 , Japan

• Shinji Tanaka

  Research Center for Materials Science, Nagoya University, Chikusa, Nagoya, Aichi 464-8602 , Japan

• Masato Kitamura

  Graduate School of Pharmaceutical Sciences, Nagoya University, Chikusa, Nagoya, Aichi 464-8601 , Japan

Abstract

[Ru(II)Cp((R)-Cl-Naph-PyCOOH)]PF6 ((R)-1) catalyzes the dehydrative cyclization of (E)-hept-2-ene-1,7-diol (2) to 2-vinyltetrahydro-2H-pyran (3) with a 97:3 S/R enantiomer ratio. Complex (R)-1 is in equilibrium between two diastereomers (R,RRu)-1 (AR) and (R,SRu)-1 (AS). A difference of turn over efficiency between the AS and AR cycles is thought to be the origin of the high enantioselectivity. The AS gives a major enantiomeric product (S)-3, according to the results of detailed mechanistic investigation via i) X-ray crystallographic analysis of related complexes, ii) NMR experiments using allylic alcohol 2, OH-lacking 2-mimic 4, d-labeled (S)-4-1d, enantiomerically enriched hept-6-ene-1,5-diol (6) as branched isomer of 2, and OH-lacking 6-mimic 5, iii) substrate structure/reactivity and selectivity relationships, iv) deuterium-labeling experiment, v) kinetics via calorimetric analysis, and vi) ligand structure/reactivity and selectivity relationships. AS captures 2 via hydrogen and halogen bonds. Oxidative addition in an H2Oin mode leads to a macrocyclic σ-allyl intermediate. Here, an efficient nC(7)OH/π*C(3)=C(2) trans-annular (TA) interaction facilitates an SN2′ nucleophilic addition of OH in an OHTA manner to furnish (S)-3. Contrary to the AS, AR cannot capture 2 using the halogen bond and slowly operates to give (R)-3. A conventional π-allyl-complex-involved mechanism is ruled out by a contradiction in the result of ii) and iii).

Journal

• Bulletin of the Chemical Society of Japan

  Bulletin of the Chemical Society of Japan 94 (2), 440-450, 2020-09-03

  Oxford University Press (OUP)

Keywords

• General Chemistry

Details

• CRID: 1360568774246435712
• NII Article ID: 130007995431
• DOI: 10.1246/bcsj.20200228
• ISSN: 13480634
• ISSN: 00092673
• Web Site: https://academic.oup.com/bcsj/article-pdf/94/2/440/56308949/bcsj.20200228.pdf
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