Neighbouring pyridine nitrogen

An interesting activation of a secondary C-H bond adjacent to the amino group of 2-(alkylamino)pyridines (184) by [(cod)2lr]BF4 has allowed an enantioselective addition across C=C and C=C bonds. The reaction is facilitated by the neighbouring pyridine nitrogen in (184) in the presence of tolylBINAP, the products (185) were obtained in moderate to 99% cc. ... 

Four crystal structures of molecules with aliphatic spacers (13b-e) and two crystal structures of molecules with the aromatic spacer -(CeUi)-, having 1,4- (13f-l) and 1,3-(13f-2) substitution, have been reported [25]. In the cases of 13b, 13c and 13f-2, amide-to-amide hydrogen bonds are not observed as the amide N-H is involved in N-H... N hydrogen bonds with pyridine-nitrogen to form a corrugated 2-D layer which has similar connectivity to the N-H...O 2-D layer (Scheme 7.4, Figure 7.16). The amide-carbonyl is involved in C-H... O contacts with neighbouring layers. 

The structure of the first complex consists of [Hg2(C5H4NCl)2]2 + cations. The mercury is co-ordinated by the basic nitrogen of the pyridine to give effectively digonal co-ordination (Hg—Hg = 2.49 A L HgHgN = 167°). Derivations from linearity and deviations of the ligands from planarity are attributed to repulsion between the chloro-substituents on neighbouring cations.178... 

Much has already been published on the irradiation of pyridine N-oxides and related compounds consistent with many observations, 6-cyanophenanthridine IV-oxide (60) was shown some years ago to give good yields of (61) on irradiation in acetone or benzene solution. In the presence of 2,3-dimethylbut-2-ene, however, irradiation of (60) produces a very different type of reaction for which there is no precedent.Thus (62) is formed in 35% yield via a process which involves cleavage of the heterocyclic ring, shift of the oxygen atom from nitrogen to the neighbouring carbon, and addition of the ethylene. 

As an illustration of the way in which hetero-atoms are, in practice, accommodated into the Hiickel scheme, we set up here the secular determinant for pyridine. Let us (arbitrarily) base it on the atomic numbering of Fig. 3.3a, in which the nitrogen atom is labelled I Then, by use of the zero-overlap approximation ( 2.3), and the assumption that matrix elements, H,s (r s), between non-nearest neighbours are zero ( 2.2), arguments similar to those outlined for butadiene in 2.7 lead to the following secular determinant for pyridine. 

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