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

✍ Scribed by Hiroshige Koide; Motokazu Uemura

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 175 KB
• Volume: 12
• Category: Article
• ISSN: 0899-0042
• DOI: 10.1002/(sici)1520-636x(2000)12:5/6<352::aid-chir9>3.0.co;2-p

✦ Synopsis

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.