Despite the near‐perpendicular arrangement of the amide group and aromatic ring in many tertiary aromatic amides, ortho‐lithiation is still a very straightforward process. The first X‐ray crystal structures of ortho‐lithiated amides reveal why: the angle of twist is lessened to some degree, and the lithium ion lies far from the plane of the aromatic ring, with stabilization of the strained structure being achieved by dimerization (see scheme).

Keywords: Density functional calculations / Diazomethane / Lithium / Solid-state structures / Solution structure (Trimethylsilyl)diazomethane (1-H) reacts with nBuLi in THF at elevated temperature to afford (previously reported) 1-Li· 3 / 2 THF. However, reaction in hexane/TMEDA at low temperature affords instead the N-lithiate Me 3 SiCNNLi·TMEDA (9), which is a novel ''open'' pseudo-cubic tetramer in the solid state. Variable-temperature NMR spectroscopy suggests that N-metallated 9, apparently the kinetic product of the reaction, irreversibly rearranges at high temperature in solution to give the thermodynamically preferred C-lithiated

Despite the near‐perpendicular arrangement of the amide group and aromatic ring in many tertiary aromatic amides, ortho‐lithiation is still a very straightforward process. The first X‐ray crystal structures of ortho‐lithiated amides reveal why: the angle of twist is lessened to some degree, and the lithium ion lies far from the plane of the aromatic ring, with stabilization of the strained structure being achieved by dimerization (see scheme).

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Reaction of n-butyllithium with Me 3 SiCHN 2 in THF affords the first example of a lithiated diazomethane with C-Li and N-Li bonds.Diazomethane, H 2 CN 2 , substituted diazomethanes, RCHN 2 , and their alkali-metallated derivatives have long had considerable use in synthetic organic chemistry. [1] Many studies, both experimental and calculational, have probed the fundamental structures of, and the bonding within, these species.[ A series of papers stretching over 35 years [2] best epitomises studies on diazomethanes. For H 2 CN 2 itself, deprotonation/reprotonation experiments detected species 1a and 1b, but not the so-called nitrile isomer 1c. Recent calculations [4] found that 1a is the most stable isomer. However, it was further calculated that for lithiated diazomethane the NϪLi species 2b (derived formally from 1b) is more stable than the CϪLi one 2a, with 2c being of yet lower stability. This already rather complicated chemistry is compounded on considering the results of metallating monosubstituted diazomethanes 3. Experimentally, it was found that here (e.g., when R ϭ Me or Ph) metallation then reprotonation could give cyclised products, the 4,5-disubstituted triazols 4-H.[2b] [2f] On the other hand, calculations on lithiated H 3 SiCHN 2 showed that the nitrile isomer 5c (akin to 2c; R ϭ H 3 Si) is slightly more stable (by 1.4 kcal mol Ϫ1 ) than the CϪLi species 5a.[4] It was thus a neat convergence of experiment and theory that lithiation of Me 3 SiCHN 2 in Et 2 O afforded a product containing both Me 3 SiCN 2 Li and lithiated cyclised units 4-Li (R ϭ Me 3 Si), viz 6.[4] The solidstate structure of 6 is complicated, but the key feature is that the lithiated diazomethane units show only NϪLi attachments and no CϪLi ones, thus supporting theory by favouring 5c over 5a.Our initial interest in lithiated (trimethylsilyl)diazomethane stemmed from its recent use in the syntheses of ynolates, the triple-bond equivalents of enolates. [5] In these syntheses, the first step is lithiation of Me 3 SiCHN 2 in THF, followed by CO insertion into the (proposed) CϪLi bond Eur.