ASYMMETRIC DIELS-ALDER CYCLO-ADDITION REACTIONS WITH CHIRAL ALPHA, BETA-UNSATURATED N-ACYLOXAZOLIDINONES
ASYMMETRIC DIELS-ALDER CYCLO-ADDITION REACTIONS WITH CHIRAL ALPHA, BETA-UNSATURATED N-ACYLOXAZOLIDINONES
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DOI：
10.1021/ja00212a037
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发表时间：
1988-02-17
影响因子：
15
通讯作者：
BISAHA, J
中科院分区：
文献类型：
--
作者：
EVANS, DA;CHAPMAN, KT;BISAHA, J
手性α,0-不饱和,'V-酰基恶唑烷酮在二烷基氯化铝促进的狄尔斯-阿尔德反应中是高反应性和高非对映选择性的亲双烯体。提出了一种阳离子路易斯酸-亲双烯体复合物来解释观察到的异常反应性和内/外选择性。带有苯丙氨醇衍生恶唑烷酮的丙烯酸酯和 (F)-巴豆酸酯甲酰亚胺在低至 100°C 的温度下与相对不活泼的二烯异戊二烯和戊间二烯进行快速和选择性环加成。 (E, F)-2, 7, 9-十碳三烯酰亚胺和 (F, F)-2, 8, 的分子内环加成10-十一碳三烯酰亚胺具有高非对映面选择性和几乎完全的内/外选择性。在所有情况下，通过简单的重结晶或硅胶色谱法可以获得高产率的非对映体均质产物。即使是空间位阻最大的狄尔斯-阿尔德加合物，也能轻松实现非破坏性手性辅助去除。在苯丙氨醇衍生的亲二烯体的狄尔斯-阿尔德反应中观察到的增强的非对映选择性被证明不是空间起源的，而是涉及苯环的电子相互作用的结果。用于揭示这种电子效应的技术，比较类似烷基化和狄尔斯-阿尔德反应中的非对映选择性，直接提供过渡态结构信息。
Chiral a, 0-unsaturated,'V-acyloxazolidinones are highly reactive and highly diastereoselective dienophiles in Diels-Alder reactions promoted by dialkylaluminum chlorides. A cationic Lewis acid-dienophile complex is proposed to account for the observed exceptionalreactivity and endo/exo selectivities. Acrylate and (F)-crotonate carboximides bearing phenylalaninol-derived oxazolidinones undergo rapid and selective cycloadditions with the relatively unreactive dienes isoprene and piperylene at temperatures as low as-100 C. Intramolecular cycloadditions of (E, F)-2, 7, 9-decatrienimidesand (F, F)-2, 8, 10-undecatrienimides proceed with high diastereoface selectivity and virtually complete endo/exo selectivity. In all cases, high yields of diastereomerically homogeneous products may be obtained by simplerecrystallization or silica gel chromatography. Nondestructive chiral auxiliary removal is facile with even the most sterically hindered Diels-Alder adducts. Theenhanced diastereoselectivities observed in Diels-Alder reactions of phenylalaninol-derived dienophiles are shown not to be steric inorigin but a result of electronic interactions involving the phenyl ring. The technique employed toexpose this electronic effect, comparison of diastereoselectivities in analogous alkylation and Diels-Alder reactions, directly provides transition-statestructural information.