Interaction, bond formation or reaction between a dimethylamino group and an adjacent alkene or aldehyde group in aromatic systems controlled by remote molecular constraints

Peri-peri interactions in naphthalene systems control the degree of bond formation between a peri-dimethylamino group and a polarised alkene or aldehyde group. Two peri-phenyl groups, which repel, induce closer N⋯C interactions or bond formation, while the ethylene link in the corresponding acenaphthene system has the opposite effect, and for the more electron-deficient alkenes lead to formation of a fused azepine ring initiated by the tert-amino effect. In related 1,8-fluorene derivatives N⋯C interactions occur for an aldehyde and a moderately polarised alkene, but fused azocines are formed when the alkene is more reactive

Modelling of an aza-Michael reaction from crystalline naphthalene derivatives containing peri–peri interactions: very long N–C bonds?

The separation between a pair of peri-located dimethylamino and ethene-2,2-dinitrile groups in a naphthalene molecule, which models the progress of a Michael reaction, can be controlled by the installation of a short ethylene bridge or the introduction of repulsive interactions at the opposite set of peri positions. Introduction of a dimethylammonium substituent produced a hydrated chloride salt in which the Me2N⋯C(H)[double bond, length as m-dash]C(CN)2 separation between reactive groups decreases, reversibly, from 2.167 Å at 200 K to 1.749 Å at 100 K, with the maximum rate of change in the range 128–140 K, which was studied by variable temperature X-ray crystallography and solid state NMR. From these and other crystallographic data a correlation between Me2N⋯C bond formation and alkene bond breaking was constructed for the first step of an aza-Michael reaction