抄録
Mn-salen catalysts (e.g. 3 and 14) were found to be effective catalysts for enantioselective oxygen-transfer reaction. Catalyst 3 showed extremely high enantioselectivity in the epoxidation of cis-olefins conjugated with aryl, alkenyl and alkynyl groups. For example, the epoxidation of 2,2-dimethylchromene and inden proceeded with high enantioselectivity of >99% ee and 98% ee, respectively, to give the corresponding epoxides that were key intermediates for the syntheses of (3S,4R)-4-amino-3-hydroxy-2,2-dimethylchromane derivatives, K-channel opener, and L-735,524, a drug for AIDs. The hypothesis on the mechanism of high asymmetric induction was also presented based on the data about the epoxidation with various types of Mn-salen catalysts. Catalyst 14 catalyzed the oxidation of aryl methyl sulfides with a good level of enantioselectivity up to 90% ee. Mn-salen catalyzed epoxidation could be successfully applied to the enantioselective synthesis of the antipode of the aggregation pheromone(21) of the flat grain beetle, cryprolestes pussilus. The synthesis started with the cross coupling reaction of cis-1-bromo-1-propene and 1-heptyne. The resulting cis-enyne 16a was subjected to the asymmetric epoxidation with Mn-salen catalyst 3 as a catalyst. The reaction gave a mixture of (2R,3S)- and (2R,3R)-epoxides which were treated with LAH without separation to give (R)-2-hydroxy-4-decyne (18a) of 86% ee. The internal acetylenic group was shifted to the terminal position by treatment with KAPA. After hydroxy protection as THP ether, the resulting terminal acetylene was carbon-extended to give 19. Deprotection of MPM ether followed by PDC oxidation and deprotection of THP ether gave hydroxy acid (20) which has been converted into 21 in two steps by Mori et al.
