New Asymmetric Catalysis by (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: 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'-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).

Chiral cationic palladium(II) 2-(phosphinophenyl)pyridine (1a) complex was found to be an effective catalyst for asymmetric Baeyer-Villiger oxidation of prochiral cyclobutanones. For example, good and excellent enantioselectivities (80% and >99% ees) were achieved in the reactions of 3-phenylcyclobutanone and a tricyclic cyclobutanone, respectively.

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