Abstracr. (Salen)manganese(M) complex 7 designed on the basis of the new proposal on the olefin's access to metal-0x0 bond and complex 10 having axial chirality in salicylaldehyde part were found to be effective catalysts for the epoxidation of unfunctional&d oletins, especially for cis-olefins.
Epoxides serve as versatile intermediates in synthetic organic chemistty, because they ate readily converted into various useful functional groups in regio-and stereoselective manners. Accordingly, many methodologies for the enantioselective synthesis of epoxides have been reported, since Henbest et al. first reported the epoxidation of styrene with peroxycamphoric acid in 1967.1) Among them, asymmetric epoxidation using a Ti(OPr-i)&Glkyl tartratelr-butyl hydroperoxide system reported by Sharpless and one of the author (T.K.) is the most useful method for the synthesis of optically active epoxides from the view point of enantioselectivity (>90% ee), mildness of the reaction conditions, and economics?) Although the scope of this reaction is very wide, substrates used is limited only to allylic alcohols and simple olefins do not undergo epoxidation under the conditions. In 1983, Davis et al. reported that optically active oxaziridine was an efficient epoxidizing agent of simple oletins. For example, epoxidation of nuns-P-methylstytene gave the corresponding epoxide of 66% ee.3) However, this reaction requires use of stoichiomettic amount of expensive oxaziridine. On the other hand, oxidation in vivo proceeds enantioselectively with aid of oxidizing enzymes such as cytochrome P-450 that has ironporphyrin complex as an active site. In order to reproduce the catalysis of P-450 in flask, many optically active metalloporphytins have been synthesized and used for the epoxidation of simple oletins.4) Epoxidation of mono-and cis-disubstituted olefins with these porphyrin complexes generally shows moderate to good level of enantioselectivity but that of rruns-olefins shows poor selectivity, except for one example.4h) Difficulty in the construction of effective porphyrin catalyst is partly attributable to its x-conjugated planar structure which does not allow the presence of stereogenic carbons in porphyrin ring. In contrast to porphyrin complex, salen complex that also serves as an oxidation catalyst can contain stereogenic carbons at Cl" and C2" and at C8 and C8' carbons (Fig. I). Since these stereogenic centers are located close to metal center, the higher asymmetric induction can be expected by using this type of optically active salen complexes as catalysts (Fig. 2).59@ Along this line, we synthesized (salen)manganese(III) complexes (l-4) and examined the epoxidation of This paper is dedicated to Professor K. Barry Sharpless and Professor Ryoji Noyori.