New asymmetric Diels-Alder cycloaddition reactions. Chiral .alpha.,.beta.-unsaturated carboximides as practical chiral acrylate and crotonate dienophile synthons
作者:D. A. Evans、K. T. Chapman、J. Bisaha
DOI:10.1021/ja00327a031
日期:1984.7
diastereometrically pure adduct in 82% yield as colorless prisms, mp 96-98 "C (Table I, entry D). The data included in Table I indicate that both chiral acrylates la-3a and crotonates lb-3b are excellent chiral dienophiles which undergo exceptionally high-yield cycloaddition reactions. Most significantly, the levels of asymmetric induction in these systems are consistantly good. From the standpoint of practicality
具有指定非对映异构体纯度的分离材料。从锂化的 2-恶唑烷酮和 (E)-2-丁烯酰氯中以 80-90% 的产率获得结晶巴豆酸酯酰亚胺 1b-3b,与之前报道的 N-酰化过程直接类比:~lb,mp 56-56.5" C;2b,mp 85-86 OC;3b,mp 66-66.5"C6 更敏感的丙烯酸酯羧酰亚胺la,mp 44-45"C;2a,73.5-74.5"C,和 3a (油)在 50-在仔细定义的条件下,来自相应的 N-溴镁 2-恶唑烷酮和丙烯酰氯(THF,0°C,5 分钟)的产率为 60%。^^' 我们对这些亲二烯体的合成效用的初步评估是与Lewis酸促进了环戊二烯的Diels-Alder过程(方案I)。经过对Lewis酸加成物的广泛调查,我们发现二乙基氯化铝 (DEAC) 或二甲基氯化铝 (DMAC) 相对于亲二烯体的用量超过 1 当量,对于实现高反应非对映选择性至关重要。在一个典型的实验中,巴豆酰亚胺