75 光学活性人工ポリ環状エーテルの分子設計を指向した二連結環状エーテルブロックの効率的不斉合成(ポスター発表の部)

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We now describe a new strategy for the two-directional, stereoselective, and asymmetric synthesis of double-tetrahydrofuran skeletons based on (i) a new type of two-directional 1,4-asymmetric hydroxyalkylation of C_2-symmetrical double β-alkoxydithianes (e.g., 3 and 4) with aldehydes leading to the syn-syn tetraols (e.g., 5a), and (ii) the efficient two-directional 1,3-asymmetric reduction of double cyclic-hemiketals (e.g., 17) with Lewis acid/R_3SiH in dichloromethane leading to the trans-trans double-tetrahydrofurans (e.g., 19a: the enantiomer of 6c). The key intermediate 2 is readily prepared with the optically active and C_2-symmetrical diepoxyde 1 which is easily obtainable from L-tartaric acid. The regioselective and stereospecific double-cyclodehydration of the tetraol isomers (e.g., 5a-c) is efficiently achieved in one-step with p-TsCl and 2,6-lutidine in pyridine to give the double-tetrahydrofurans (e.g., 6a-c: the enantiomers of 19a-c), without concomitant of any other isomers, respectively.
天然有機化合物討論会の論文
1993-09-10