Nonreductive Enantioselective Ring Opening of<i>N</i>-(Methylsulfonyl)dicarboximides with Diisopropoxytitanium α,α,α′,α′-Tetraaryl-1,3-dioxolane-4,5-dimethanolate
作者:Diego J. Ramón、Gabriela Guillena、Dieter Seebach
DOI:10.1002/hlca.19960790328
日期:1996.5.8
dicarboximides 1a–f are converted enantioselectively to isopropyl [(sulfonamido)carbonyl]-carboxylates 2a–f by diisopropoxytitanium TADDOLate (75–92% yield; see Scheme 3). The enantiomer ratios of the products are between 86:14 and 97:3, and recrystallization from CH2Cl2/hexane leads to enantiomerically pure sulfonamido esters 2 (Scheme 3). The enantioselectivity shows a linear relationship with the
二环丙氧基钛TADDOLate将双环和三环内消旋-N-(甲基磺酰基)二甲酰亚胺1a-f对映体转化为异丙基[(磺酰胺基)羰基]-羧酸盐2a-f(产率为75-92%;参见方案3)。产物的对映体比例在86:14至97:3之间,并且从CH 2 Cl 2 /己烷中重结晶得到对映体纯的磺酰胺基酯2(方案3)。对映选择性与所用TADDOL的对映体过量显示线性关系(图3)。还原酯基和羧酰胺基(LiAlH 4)和酰亚胺开环的产物2中磺酰胺基(Red-Al)的额外还原裂解分别得到羟基磺酰胺3和氨基醇4(流程4)。磺酰胺基酯2的绝对构型是通过化学相关性(与2a,b;方案6),对3e的樟脑酸酯的X射线分析(图1)以及对羟基苯甲酸酯的19 F-NMR分析确定的羟基磺酰胺3的较硬酯(表1)。对于伯醇和胺的的绝对构型的分配的一般建议式HXCH 2 CHR 1 - [R 2,X = O,NH,建议(见11在表1中)。从2