Synthesis of axially chiral benzamides utilizing tricarbonyl(arene)chromium complexes

Axially chiral N,N-diethyl 2,6-disubstituted benzamides were stereoselectively 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 8-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. (C) 2000 Wiley-liss, Inc.