Koide H, Uemura M
Department of Chemistry, Faculty of Integrated Arts and Sciences, Osaka Prefecture University, Sakai, Osaka, Japan.
Chirality. 2000 Jun;12(5-6):352-9. doi: 10.1002/(SICI)1520-636X(2000)12:5/6<352::AID-CHIR9>3.0.CO;2-P.
Axially chiral N,N-diethyl 2,6-disubstituted benzamides were stereo-selectively prepared utilizing planar chiral (arene)chromium complexes as an enantiomerically active form by following two methods. Ortho-lithiation of the enantiomerically pure planar chiral tricarbonyl(N,N-diethyl 2-methylbenzamide)chromium complex followed by electrophilic quenching gave axially chiral 2-methyl-6-substituted N,N-diethyl benzamide chromium complexes. Photo-oxidative demetalation produced the chromium-free axially chiral benzamides as optically active compounds. An alternative method for the preparation of axial chiral benzamides is an enantioselective lithiation at the benzylic methyl of meso tricarbonyl(N,N-diethyl 2,6-dimethylbenzamide)chromium with appropriate chiral lithium amide base followed by quenching with alkyl halides.
通过两种方法，利用平面手性（芳烃）铬配合物作为对映体活性形式，立体选择性地制备了轴向手性N,N-二乙基-2,6-二取代苯甲酰胺。对映体纯的平面手性三羰基（N,N-二乙基-2-甲基苯甲酰胺）铬配合物进行邻位锂化，然后进行亲电淬灭，得到轴向手性2-甲基-6-取代N,N-二乙基苯甲酰胺铬配合物。光氧化脱金属反应生成了无铬的轴向手性苯甲酰胺，为光学活性化合物。制备轴向手性苯甲酰胺的另一种方法是用适当的手性酰胺锂碱对内消旋三羰基（N,N-二乙基-2,6-二甲基苯甲酰胺）铬的苄基甲基进行对映选择性锂化，然后用卤代烃淬灭。
