P-47 テトロン酸のキレーション制御求核付加反応とその天然物合成への応用(ポスター発表の部)
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The aldol reaction has been recognized as one of the most promising methods for selective carbon-carbon bond formation, in which chelation control has also been established to play an important role to determine the stereochemistry of the resulting hydroxy group. As tetronic acid seems to be a useful building block in natural product synthesis, we investigated the aldol reaction of tetronic acid and its derivatives with carbonyl compounds. The aldol reaction of tetronic acid dianion (4), prepared from various metal bases, with ketone (5) provided the anti adduct (6) predominantly. These results clearly suggested that the reaction proceeded via six-membered chelation transition model (C). The aldol reaction of methoxymethyl tetronate (9a) with (R)-2,3-O-cyclohexylideneglyceraldehyde (12) afforded arabino- and ribo-type compounds in a ratio of 4.2:1 (81.1% yield). This stereoselectivity can be rationalized by assuming that this reaction proceeded through the sterically favored chelation model (F) as a transition state to give arabino-type adduct (13) rather than the transition state (G) leading to the formation of ribo-type compound (14). The stereochemistries of the arabino- and ribo-compounds were unambiguously determined by their conversion into the penta-acetates of arabitol and ribitol. The method developed above was successfully applied to the synthesis of the B-ring moiety (37) of sesbanimide A (26) and B (27), potent antitumor compounds isolated from the seeds of Sesbania drummondii and Sesbania punicea, and the synthetic intermediate (49) of restricticin (38), anti fungal agent, isolated from Penicillium sp.. The nucleophilic addition reaction of tetronic acid dianion (50) to imines was also investigated to give the syn adduct (51) stereoselectively. The stereoselectivity observed in the formation of the syn adduct can be rationalized by assuming that this addition proceeded via a six-membered chelation transition state (H).
- 天然有機化合物討論会の論文
- 1995-09-01
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