New Asymmetric Catalysis by (Salen)cobalt(III) Complexes (Salen=[Bis(salicylidene)ethylenediaminato]={{2,2′-[ethane-1,2-diyl]bis[(nitrilo-κN)methylidyne]bis[phenolato-κO]}(2−)}) of cis-β-Structure: Enantioselective Baeyer-Villiger Oxidation of Prochiral Cyclobutanones
✍ Scribed by Tatsuya Uchida; Tsutomu Katsuki; Katsuji Ito; Suemi Akashi; Ayako Ishii; Tomomi Kuroda
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- German
- Weight
- 135 KB
- Volume
- 85
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
This paper is dedicated with admiration and respect to Professor Dieter Seebach on the occasion of his sixty-fifth birthday A series of chiral (salen)cobalt(III) complexes (salen [bis(salicylidene)ethylenediaminato] {{2,2'-[(ethane-1,2-diyl)bis[(nitrilo-kN)methylidyne]bis[phenolato-kO]}(2 À)}) of cis-b structure were prepared and used for the enantioselective Baeyer-Villiger oxidation of prochiral cyclobutanones with hydrogen peroxide as terminal oxidant. Both cationic (salen)cobalt(III) and neutral iodo(salen)cobalt(III) complexes 3 ± 5 and 7 ± 12, respectively, all having a chiral binaphthalenediamine unit, were found to be effective catalysts for the enantioselective Baeyer-Villiger oxidation (Tables 1,3, and 4). In particular, complex 8 bearing electronwithdrawing F-atoms showed a good level of enantioselectivity (75 ± 79% ee) in the reactions of 3arylcyclobutanones (Scheme 4). On the other hand, complex 12 bearing t Bu groups at C(3) and C(3') and electron-withdrawing NO 2 groups at C(5) and C(5') (trivial numbering) exhibited a high enantioselectivity of 98% ee in the reaction of a tricyclic cyclobutanone (Table 4).