Diels-Alder反應之外向加成

Abstract

由於 Diels-Alder 反應受到二級軌域效應的影響，因此在過去的文獻中大部分以內向加成產物為主要產物。而本篇論文想要探討在路易士酸催化條件以及加熱條件下進行 Diels-Alder 反應時，二烯化合物與親二烯基化合物之取代基效應對外向選擇性的影響，其中以 1,4-雙甲基二烯化合物與 4-苯基二烯化合物對酯類與醛類親二烯基化合物進行研究。實驗結果顯示，酯類的例子中在路易士酸催化條件下，當親二烯基化合物 bata 位置上有取代基時，反應傾向以外向加成進行，而在加熱條件下不論親二烯基化合物 beta 位置上是否有取代基，反應皆傾向形成外向加成產物為主；醛類的例子中在加熱條件下，當親二烯基化合物 beta 位置上有取代基時，反應傾向以外向加成進行，相反的，當親二烯基化合物位置上沒有取代基或是 alfa 位置上有取代基時，皆有利於內向加成的進行。最後本篇論文再與酮類、腈類以及硝類等不同拉電子基之親二烯基化合物的例子進行立體選擇性之比較。

According to previous studies, Diels-Alder reactions prefer the formation of endo cycloadducts as an effect of secondary orbital interaction. In this study, the substrate controlled exo-selectivity of Diels-Alder reactions of 1,4-dimethyl- and 4-phenylsilyl enol ether as dienes with several ,-unsaturated esters and aldehydes as dienophiles under Lewis acid catalyzed and thermal conditions was investigated. Our results show that for the ester-substituted dienophiles, under the Lewis acid catalyzed condition, the -substituted compounds favor exo-selectivity; whereas under thermal condition, the ester-substituted dienophiles favor exo-selectivity no matter the ester dienophile is substituted or not. In contrast, under thermal condition, endo addition is favored for aldehyde dienophiles with -substituents or without -substituents. Finally, we will compare the stereoselectivity of Diels-Alder reaction using dienophiles with different electron withdrawing groups such as keto, cyano and nitro groups.