The Molecular Design of Chiral Crown Ethers as Efficient Asymmetric Catalysts.

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The design of efficient catalysts for asymmetric reactions has been a recent focus in synthetic organic chemistry.Crown ethers are anticipated to be efficient catalysts for C-C bond formations, because they have been proved to complex with metal cations and activate counteranions.The asymmtric Michael, - addition of methyl phenylthioacetate 2 to 2 - cyclohexenone 3 is a good reaction to obtain optically active delta - ketoester derivative (4). The optical purity of C-3 position of 4 was determined by conversion of 4 to 5, the reductive desul-furization with (nBu)_4 SnH in a good yield. We have found that C_2-svmmetric 1 complexed with KOtBu (10mol%) catalyzes the Michael reaction of 2 and induces the relatively high enantioselectivity(71%e. e. S).