P-62 Pd(II)触媒を用いたスピロケタール環の新規構築法の開発とspirofungin Aの合成(ポスター発表の部)

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We recently reported the intramolecular substitution of an allyl alcohol by a heteroatom using a palladium (II) catalyst without activation of the allylic alcohol. We report here highly stereoselective intramolecular cyclization of 1,11-dihydroxyundece-9-en-5-one derivatives using palladium (II) catalyst via unstable hemiacetal intermediates, in which cyclization occurs without activation of the allylic alcohol to afford spiroketal structures. Spirofungin A is a polyketide-type antibiotic isolated from Streptomyces violaceusniger Tu 4113. Now we show a synthesis of spirofungin A using the cascade cyclization of ketone 7 as a key reaction. Retrosynthetic fragmentation of spirofungin A affords three segments. Firstly, we synthesized the aldehyde segment 8 from 2-butyne-1,4-diol (Scheme 5). The sulfone segment 9 was prepared from methyl (R)-3-hydroxy-2-methylpropionate (13) (Scheme 6). The cyclization precursor 7 was prepared by using Julia coupling reaction between aldehyde segment 8 and sulfone segment 9 (Scheme 7). The key cascade cyclization of 7 was achieved successfully by treatment with PdCl_2(PhCN)_2 and MeOH at room temperature to give the segment B (Scheme 8). Studies on the connection of the segment B and the segment A and C to construct the whole structure of spirofungin A are now underway
天然有機化合物討論会の論文
2005-09-15