P-68 Pd(II)触媒を用いた新規ヘテロ環構築法の開発と糖類の合成(ポスター発表の部)

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We recently developed a cyclization via a hemiacetal intermediate using a palladium catalyst and found a stereoselective method for construction of trisubstituted tetrahydropyran. In connection with the palladium-catalyzed heterocyclization, we applied the method to synthesis of a natural product having a δ-lactone structure. However the 1,3-chirality transfer using Pd(II) catalyst was uncertain. We have examined the stereochemical integrity during Pd(II)-catalyzed cyclization using 7-hydroxytridec-5-enal. Firstly, we synthesized the cyclized precursor 6E, 6Z from 1,5-pentanediol. Treatment of the cyclized precursor 6E, 6Z with 10mol% of PdCl_2(PhCN)_2 catalyst and 3 equiv. of alcohol in THF furnished the cyclized products 7 in 46-86% yield as a mixture of acetals. We proposed the stereochemistry of the acetals to lead it to a δ-lactone 8. The cyclization reaction has been found to occur highly stereoselectively with retention of configuration. To demonstrate the synthetic potential of this method, we have synthesized furanose derivatives. The optically active aldehyde 17 was prepared from 1-malic acid in 8 steps. Treatment of the aldehyde 17 and methanol with Pd(II) catalyst gave the cyclized product 18 Finally, oxidation, reduction, and deprotection of 18 was afforded 2-deoxy-D-ribose. We also synthesized 2-deoxy-L-ribose in completely another method.
天然有機化合物討論会の論文
2006-09-15