Enantiomerically pure vinylketene acetals in the Diels-Alder reaction. Catalysis and facial selectivity.
作者:Mark A. Bochler、Joseph P. Konopelski
DOI:10.1016/s0040-4020(01)86459-0
日期:1991.1
diastereoselective dienes in the Diels-Alder reaction have been developed. Most selective are (4R, 5R)-4,5-diphenyl-2-(2-methyl-2-propenidene)-1,3-dioxolane (8) and (4R, 5R)-4,5-diphenyl-2-((E)-2-butenidene)-1,3-dioxolane (9), which utilize phenyl rings as asymmetric directing groups. It was shown through NOE analysis that the major product obtained from the reaction of diene 9 and N-methylmaleimide
已经开发了一系列对映体纯的乙烯基乙烯酮缩醛,其在Diels-Alder反应中起非对映选择性二烯的作用。选择性最高的是(4 R,5 R)-4,5-二苯基-2-(2-甲基-2-亚丙烯基)-1,3-二氧戊环(8)和(4 R,5 R)-4,5-二苯基-2-((E)-2-丁烯)-1,3-二氧戊环(9),其利用苯环作为不对称的导向基团。通过NOE分析表明,由二烯9和N-甲基马来酰亚胺反应获得的主要产物是由于亲二烯体向二烯的Re exo途径,其中两个内过渡态也以少量出现在产物混合物中。确定过渡态能量的相对顺序为Re exo < Re endo < Si endo < Si exo。分子力学和π电荷密度计算均用于合理化在二烯8与N-甲基马来酰亚胺(48:1)反应中观察到的高非对映选择性。