有機不對稱連鎖反應:以硝基共軛炔烯與羥基香豆素合成(Z)-2-亞甲基吡喃

Abstract

運用有機催化劑建構高光學純度的掌性分子於不對稱反應有顯著的貢獻，以往共軛炔烯系統研究於文獻中，鮮少被探討並常需藉助金屬催化進行有機不對稱連鎖反應。本實驗利用有機催化共軛炔烯反應，以雙官能之奎寧-方醯胺催化劑進行催化，透過支鏈硝基共軛炔烯與4-羥基香豆素進行反應，並接續加入1,4-二氮雜二環[2.2.2]辛烷，進行重烯構成/Oxa-Michael/烯異構化連鎖反應，獲得環化吡喃之架構產物，其產率（up to 88%）、選擇性（> 20:1 dr）、鏡像選擇性表現優異（up to 99% ee）。

Enantioselective organocatalysis has contributed significantly to asymmetric synthesis by delivering highly functionalized complex structural entities with multiple stereogenic centers in high optical purity. Most of enyne system in previous literature was studied to establish by using synergistic/sequential metal catalysis, but it was the few on organic asymmetric cascade reaction. The organocascade reaction was established between 1,3-nitro enynes and 4-hydroxy coumarin to afford pyrano-annulated scaffolds in high yields (up to 88% yield) and excellent stereoselectivities (up to >20:1 Z:E and >99% ee) under bifunctional quinine derived squaramide and DABCO catalysis. The reaction proceeded through sequential conjugate addition, allene formation, intramolecular oxa-Michael 6-endo-dig cyclization and DABCO catalyzed olefin isomerization.