High Stereoselectivity and Facial Selectivity in Diels−Alder Cycloadditions of Novel Captodative Olefins: α-Alkoxyvinyl(ethoxy)carbene Chromium Complexes with Cyclopentadienes
作者:Miguel A. Vázquez、Liliana Cessa、José Luis Vega、René Miranda、Rafael Herrera、Hugo A. Jiménez-Vázquez、Joaquín Tamariz、Francisco Delgado
DOI:10.1021/om0343317
日期:2004.4.1
5 with 1 were found to be highly stereoselective, favoring the endo adduct at a much higher level than that observed for the analogous α-alkoxy-α,β-unsaturated esters, whereas complex 6E showed low reactivity. When 1,2,3,4,5-pentamethylcyclopentadiene (7) was employed, the cycloadditions with α-alkoxyvinyl(ethoxy)carbene complexes 3−6E were highly anti/exo selective. The exo adducts form new alkoxy-chelated
新型Fischer卡宾配合物(CO)5 Cr C [C(CR (CHR')(OR)] OCH 2 CH 3(3,R'= H,R = CH 2 CH 3 ; 4,R '= H,R = CH 2 CH 2 CH 3 ; 5,R'= H,R = CH 2 CH 2 CH 2 CH 3 ; 6,R'= CH 3(E和Z),R = CH 2 CH 3)是在Diels-Alder环加成反应中与环戊二烯(1)和1,2,3,4,5-五甲基环戊二烯(7)一起进行的。(乙氧基)卡宾配合物的α烷氧基乙烯基之间的环加成3,4,和5与1被认为是高度立体选择性,有利于内切在比用于类似α -烷氧基- α观察到高得多的电平的加合物,β-不饱和酯,而配合物6 E显示出低反应活性。当1,2,3,4,5-五甲基环戊二烯(7被使用),用α-烷氧基乙烯基的环加成(乙氧基)卡宾配合物3 - 6 ë具有高度的抗/异源选择性。所述外型加