The Tertiary Amide as an Effective Director of Ortho Lithiation

Article abstract of DOI:10.1021/jo00340a008

The tertiary amides N,N-diethylbenzamide (1) and N,N-diisopropylbenzamide (3) give the ortho-lithiated species 2 on treatment with sec-BuLi/TMEDA or n-BuLi/TMEDA, respectively, at -78 deg.Lithiation of 1 followed by rection with either methyl iodide, ethyl iodide, benzophenone, acetone, benzaldehyde, or trimethoxyborane-hydrogen peroxide gives the expected ortho substituted product.Intramolecular competition between the diethyloamido and chloro, methoxyl, sulfonamido, (dimethylamino)methyl, or oxazolino functions in ortho- and para-substituted benzamides establishes the tertiary amido group to be more effective in directing metalation than any noncarboxamide functional group under the prescribed conditions.Complimentarity of directing effects is observed with the chloro and methoxyl groups in the meta-substituted diethylbenzamides but not with the methyl group.The secondary amide is found to have a directing ability comparable to the tertiary amide with sec-BuLi/TMEDA at -78 deg in THF although the yields are low. 13C NMR chemical shifts are particularly useful for the structural assignments which are confirmed chemically by lactonization of some products.A labeling study with N,N-diisopropyl-2,6-dideuteriobenzamide suggests that lithiation of the ortho position of 3 is direct and not the result of rearrangement of an initially formed α-aza anion.Control of metalation at the ortho or benzylic position by proper selection of the organolithium base is illustrated for N,N-diisopropyl-p-toluamide.The value of the tertiary amide for control of ortho lithiations and regiospecific aromatic substitutions is noted.