69 ビニロキシボラン-イミン縮合反応を利用した有用生理活性天然物の合成研究
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Thienamycin (1) has attracted a great deal of synthetic efforts because of their unique structure and broad-spectrum antibacterial activity. Although elegant syntheses of thienamycin have been reported, more efficient and highly stereoselective synthesis is still required. In the synthesis of thienamycin, 3(R)-hydroxybutyric acid was considered to be a good candidate for the chiral precursor. Success of this approach required development of the methodology for the highly stereoselective aldol type condensation of an ester enolate with an imine. We developed a vinyloxyborane-imine condensation reaction and applied it to a synthesis of thienamycin. The vinyloxyborane prepared from 6 by the use of 9-BBN triflate and diisopropylethylamine reacted with the imine 5 to give the β-benzylamino thiol ester 7, which was converted to the β-lactam 9. The major stereoisomer (ca. 90% selectivity) was found to be desired one for the synthesis of thienamycin. The fully protected β-lactam 9 was transformed to 3, a key intermediate for (+)-thienamycin. We also investigated the synthesis of 1β-methylcarbapenem (2). The β-lactam 22, which was prepared from 6 and imine 21, was converted to the key intermediate 25 by a following couple of novel reactions, a palladium catalyzed hydroesterification of terminal acetylene (22→23) and a stereoselective reduction of α,β-unsaturated ester with L-Selectride in sec-BuOH-THF (23→24).
- 天然有機化合物討論会の論文
- 1986-09-09
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- 69 ビニロキシボラン-イミン縮合反応を利用した有用生理活性天然物の合成研究