Synthesis of 3,5-Anhydro-2-deoxy-1,4-glyconolactones by Palladium(II)-Catalyzed, Regioselective Oxycarbonylation of C<sub>5</sub>- and C<sub>6</sub>-Enitols. ω-Homologation of Aldoses to Produce Intermediates for<i>C</i>-Glycoside/<i>C</i>-Nucleoside Synthesis
作者:Tibor Gracza、Thomas Hasenöhrl、Ulrich Stahl、Volker Jäger
DOI:10.1055/s-1991-28400
日期:——
The palladium(II)-catalyzed oxycarbonylation, known with alkenols and alkenediols, is studied with optically active 4-pentenitols (-triols) 1, 7 and 5-hexenitols (-tetrols) 12, 15, 18. Efficient routes for the substrates are provided, mostly from carbohydrate precursors. In all cases, bicyclic 3,6-anhydro-2-deoxy-1, 4-glyconolactones, versatile intermediates of C-glycosidic structure, are isolated with high selectivity and in good yield (53-77%). Several minor products (4-14% of regio-/diastereoisomers) from two competing pathways are observed and identified. The oxycarbonylation of alkenitols thus completes a novel sequence that transforms aldoses into homologous anhydro-glyconolactones, by C1-elongation at the terminal site. In the key step, the 3,4-threo arrangement is produced, from each of the four diastereomeric alkenitols studied (of the 6 cases available in the C5 and C6 series). The stereochemical protocol is summarized, e.g., by the transition D-gluco (aldose) → D-xylo (hexenitol, 15) → L-ido (anhydro-deoxyheptenolactone 26), as demonstrated.
使用钯(II)催化氧羰基化己烯醇和烯二醇已知的方法,研究了光学活性的4-戊烯氮醇(三醇)1、7和5-己烯氮醇(四醇)12、15、18。提供了一种高效的路径,大部分以碳水化合物为底物。在所有情况下,双环3,6-脱水-2-脱氧-1,4-甘露环酮,C-糖苷结构的多种中间体,均以高选择性和较好的产率被分离出来(53-77%)。观察和识别了来自两个竞争途径的数个次要产品(4-14%的位/对映异构体)。烯氮醇的氧羰基化完成了一个将醛糖转化为同源脱水甘露醇环酮的新序列,通过在末端位点的C1延伸。在关键步骤中,从所研究的四种差向异构的烯醇(C5和C6系列共有6个)中,每个都产生了3,4-苏型排列。例如,通过D-葡萄糖(醛糖) → D-木糖(己烯醇,15) → L-艾杜糖(脱氧庚烯环酮26)这样的过渡,来证明立体化学的规程。