20 触媒的メソアシンメトリゼーション法の開発と天然物合成への活用(口頭発表の部)

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Chiral BINAP-Rh(I)-catalyzed asymmetric desymmetrization (asymmetrization) of a series of the tricyclic meso-1,4-enediols and their bis-ethers having bicyclo[2.2.1]heptane and bicyclo[2.2.2]octane background has been examined for the construction of versatile chiral building blocks served as chiral cyclohexenone and chiral cyclohexadienone. The isomerization reaction occurred facilely to give the keto-alcohols or the keto-ethers in excellent yields with high optical purities when the bis-ethers were used as substrates though the products from the alcohols did not have high optical purities. Interestingly, the optical specificities observed between the alcohols and the ethers were inversed in the presence of the same chiral BINAP-Rh(I) catalyst. The reaction was confirmed to proceed via a suprafacial 1,3-hydrogen migration by deuterium labeling experiment. The reaction was also extended to the isomerization of a monocyclic seven membered meso-1,4-enediol bis-silyl ether which afforded the optically active hydroxy-ketone in an excellent yield with moderate optical purity (〜70%ee). The chiral monocyclic product thus obtained was utilized for the first enantiocontrolled synthesis of the tropane alkaloid (-)-physoperuvine The resulting optically enriched tricyclic products having bicyclo[2.2.1]heptenene background were used as a versatile chiral building block serving as chiral cyclohexenoids and chiral cyclohexadienoids. Namely, owing to their rigid biased framework, they allowed diastereoselective modification from convex face and, moreover, they generate the double bond by thermal retro-Diels-Alder reaction making themselves as versatile chiral building blocks. Their potential as chiral building blocks were demonstrated by diastereo- and enantiocontrolled construction of a variety of natural products and their key intermediates ranging from a simple monoterpenoid to a complex steroid molecule, such as 4-hydroxy-2,6,6- and 4-hydroxy-3,5,5-trimethyl-2-cyclohexenones, malingolide, isoretronecanol, tracheranthamidine, shikimic acid, tricholomenyn A, calcitriol A ring, etc.
天然有機化合物討論会の論文
1997-07-20

20 触媒的メソアシンメトリゼーション法の開発と天然物合成への活用(口頭発表の部)

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