Hetero Diels-Alder Reactions of Nitroso Alkenes with Alkoxyallene Derivatives Bearing Carbohydrate Auxiliaries: Asymmetric Synthesis of 6<i>H</i>-1,2-Oxazines and Subsequent Reductive Transformations
作者:Hans-Ulrich Reissig、Reinhold Zimmer、Beate Orschel、Stefan Scherer
DOI:10.1055/s-2002-33328
日期:——
Alkoxyallene derivatives 1a-f bearing carbohydrate auxiliaries at the oxygen were examined in asymmetric hetero Diels-Alder reactions with nitroso alkenes. Diacetoneglucose derived compound 1a turned out to be the best precursor furnishing the primary cycloadducts 3a-c with a diastereomeric ratio of approximately 90:10. Isomerization provided the thermodynamically more stable 6H-1,2-oxazines 4a-c. Similarly, diacetonefructose derived allene 1f gave compounds 4h-j with good efficiency. Gratifyingly, it turned out that 1a and 1f were complementary with respect to the preferential absolute configuration at C-6 of 6H-1,2-oxazines 4a-c and 4h-j, respectively. Cycloadducts derived from 1a have 6S configuration in excess whereas those derived from 1f are predominantly 6R configured. Exhaustive hydrogenolysis of 6H-1,2-oxazines 4a and 4h in the presence of palladium on charcoal furnished the expected primary amine 5 in an enantioenriched form. If this reduction was performed under addition of hydrochloric acid, pyrrolidine derivative 6 together with secondary amine 7 as side product were isolated.
在与亚硝基烯的不对称杂环 Diels-Alder 反应中,研究人员考察了在氧位上含有碳水化合物助剂的烷氧基烯衍生物 1a-f。结果表明,二丙酮葡萄糖衍生的化合物 1a 是最好的前体,可以产生初级环加载物 3a-c,非对映比率约为 90:10。异构化反应产生了热力学上更稳定的 6H-1,2-噁嗪 4a-c。同样,二丙酮果糖衍生的烯 1f 也能高效地生成化合物 4h-j。令人欣慰的是,1a 和 1f 分别在 6H-1,2-噁嗪 4a-c 和 4h-j 的 C-6 绝对构型上具有互补性。由 1a 生成的环加载产物具有过量的 6S 构型,而由 1f 生成的环加载产物则主要具有 6R 构型。在木炭上的钯存在下,对 6H-1,2-噁嗪 4a 和 4h 进行彻底氢解,可以得到预期的对映体形式的伯胺 5。如果在加入盐酸的情况下进行还原,则可分离出吡咯烷衍生物 6 和作为副产物的仲胺 7。