80(P-79) Pd(II)触媒を用いたヘテロ環化反応の立体選択性とPrelactone Cの合成研究(ポスター発表の部)

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The polysubstituted δ-lactone structure can be found in many natural products, particularly polyketide macrolide producing microorganisms. It is a very important to develop synthetic methodology for the stereoselective construction of the δ-lactone structure. We recently developed a cyclization via a hemiacetal intermediate using a palladium catalyst and found a stereoselective method for construction of trisubstituted tetrahydropyran (Scheme 1). In connection with the palladium-catalyzed heterocyclization, we applied the method to synthesis of a natural product having a δ-lactone structure. We planned the synthesis of (+)-prelactone C, which comprises an important class of highly functionalized chiral δ-lactones and was isolated from the concanamycin-producing Streplornyces sp. Now we show a synthesis of (+)-prelactone C using palladium catalyzed cyclization of aldehyde 20 as a key reaction. Firstly, we synthesized the cyclized precursor 20 from propargyl alcohol (Scheme 3,4,5,6). Treatment of the aldehyde 20 with 10 mol% of PdCl_2(PhCN)_2 catalyst and 2.2 equiv. of MeOH in THE furnished the cyclized products 21 in 80% yield as a mixture of acetals. We proposed the stereochemistry of 21 to lead it to the lactone 23. The relative stereochemistry of 23 was established by the coupling constant of its ^1H NMR spectrum. Surprisingly, the spectra of the obtained compound 23 were not found to be identical to that of natural (+)-prelactone C. This was not entirely unexpected, as 23 was an epimer at the C-5 position of prelactone C.
天然有機化合物討論会の論文
2004-10-01

80(P-79) Pd(II)触媒を用いたヘテロ環化反応の立体選択性とPrelactone Cの合成研究(ポスター発表の部)

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