34 ワンポットアザ電子環状反応を利用した新規合成法の開発と天然物合成への展開(口頭発表の部)

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In a previous study, we found the significant acceleration of 6π-azaelectrocyclization by the obvious substituent effect due to the presence of a pair of C4-electron-withdrawing and C6-conjugating substituents in azatrienes to quantitatively produce the corresponding dihydropyridines. Based on this discovery, we have established the highly stereoselective asymmetric 6π-azaelectrocyclization using a chiral 7-isopropyl-cis-aminoindanol derivative 6, and moreover, we developed a one-pot asymmetric azaelectrocyclization protocol using vinylstannane, iodoolefin and aminoindanol as starting materials with high diastereoselectivity. Herein, to the further development of this one-pot reaction, we report novel synthetic methods for 2,4-disubstituted pyridines and 2,4,5-trisubstituted-2,5-chiral piperidines. At first we present a highly efficient and novel synthetic method of 2-arylpyridines using our own one-pot 6π-azaelectrocyclization followed by a base treatment. Thus, this method includes a sequence that consists of the coupling of three components (methanesulfonamide 1, vinylstannane 2, and iodoolefin 3) in the presence of a palladium catalyst, generation of dihydropyridine by smooth 6π-azaelectrocyclization, followed by aromatization by a treatment with DBU. This strategy has high generality to various vinylstannanes. In addition, more efficient pyridine synthesis on solid supports using sulfonamide resin 4 is also reported. Next, we present a useful method of the construction of the 2,4,5-trisubstituted-2,5-chiral piperidine skeleton via one-pot asymmetric 6π-azaelectrocyclization using a tetrasubstituted olefin 15, vinylstannanes 2 and aminoindanol 6. The new chiral center at C5 is completely controlled due to the thermodynamic stability of the resulting tetracyclic products containing the aminoindanol structure. This strategy also shows high generality to various vinylstannanes, which leads to successful applications to asymmetric total syntheses of two indole alkaloids: 20-epiuleine and (-)-corynantheidol.
2008-09-01

34 ワンポットアザ電子環状反応を利用した新規合成法の開発と天然物合成への展開(口頭発表の部)

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