John W. Davies

Preparation and spectroscopic studies of the 1,4-dihydro- 1,4-iminonaphthalene (7-azabenzonorbornadiene) ring system

Abstract The synthesis of a range of N-alkyl 1,4-dihydro-1,4-iminonaphthalenes (7-azabenzonorbornadienes) and reduced derivatives is described together with 1,4-dihydro-1,4- and 9,10-dihydro-9,10- iminoanthracenes. VT NMR studies lead to unambiguous assignment of invertomer preferences; changes in the invertomer ratios and nitrogen inversion barriers are investigated as the electronic and steric environment is modified by variation of substituents in the carbon skeleton and at nitrogen.

Electronic control of stereoselectivity in the chlorination of 1,4-dihydro-1,4-iminonaphthalenes (7-azabenzonorbornadienes) with N-chlorosuccinimide

Abstract Chlorination of a range of secondary amines based on the 1,4-dihydro-1,4-iminonaphthalene (7-azabenzonorbornadiene) ring system is described. At low temperatures, the ratio of syn- and anti- N-chloroamines formed under conditions of kinetic control can be determined; this ratio is shown to be influenced substantially by variation in the electronic character of the aryl ring. At higher temperatures, inversion at nitrogen leads to different (thermodynamic) invertomer ratios which also vary as a function of substitution. Substituents in the aryl ring and in the bicyclic skeleton also influence the nitrogen inversion barrier.

15N nuclear magnetic resonance studies of azabicycles : unusual deshielding of nitrogen in the 7-azabicyclo[2.2.1]heptyl ring system

Abstract 15N-enriched samples of derivatives of the 7-azabicyclo[2.2.1]heptyl system were synthesised and 15N NMR spectra were recorded using 15N-enriched and natural abundance samples; separate signals were observed for the two invertomers in N-methyl and N-chloro derivatives. Considerable deshielding was observed in comparison with simple amines and with 8-azabicyclo[3.2.1]octyl and 9-azabicyclo[4.2.1]nonyl analogues. Predictable changes in chemical shift resulted from substitution at nitrogen and at α-carbons; the effects of configuration at nitrogen, of unsaturation, and of substitution further from the nitrogen were also explored.

Heterolysis of N-chloro-1,2,3,4-tetrahydro-1,4-iminonaphthalenes and related systems; effects of structure and of solvent on reaction pathways

Abstract Replacement of hydrogen by methyl at the 1,4-positions of 1,2,3,4-tetrahydro-1,4-iminonaphthalenes substantially modifies the Ag(I)-catalysed solvolytic behaviour of this system giving tetrahydrobenzazepine derivatives; small amounts of methanol in non-polar solvents have a profound effect favouring heterolytic, rather than homolytic, NCl cleavage. Methanoquinolines are produced via secondary rearrangement. Bridgehead methyl substituents also divert the reactions of N-chloro-1,4-dihydro-1,4-iminonaphthalenes, leading to quinoline derivatives.

Barriers to inversion at nitrogen in bicyclic amines and hydrazines

Abstract Nitrogen inversion barriers have been measured for 7-chloro-1,7-diazabicyclo-[2.2.1] heptane and [2.2.2]octane; the unusual nature of the bridging nitrogen in bicyclo [2.2.11 systems is discussed.

Aryl participation in methanolysis of N-chloro-1,4-dihydro-1,4-iminonaphthalenes (7-azabenzonorbornadienes) and derivatives

Abstract Routes to derivatives of the 6,7-benzo-1-azabicyclo[3.2.0]heptyl ring system are described; the relative ability of substituted aryl rings to participate in selective reaction of the anti - invertomers of the title compounds during Ag(I)-catalysed methanolysis reactions is estimated qualitatively. The intrusion of N-Cl homolysis during methanolysis in some cases can be suppressed completely by the use of an Ag(I) salt together with a minimal quantity of methanol in a non-polar solvent, giving heterolysis products in excellent yield.

Unusual deshielding of 15N in bicyclic amines and hydrazines

Abstract The bridging nitrogen in 7-aza- and 1,7-diazabicyclo[2 2.1]heptanes and unsaturated derivatives shows unusually large deshielding in the 15 N NMR.

Formal dyotropic rearrangements of N-chloroamines catalysed by alumina

Rearrangement of N-chloro-2-azabicyclo[2.2.1]heptanes, [2.2.1]hept-5-enes, and [2.1.1]hexanes involving 1,2-migration of an sp3 or an sp2 carbon to nitrogen accompanied by 2,1-migration of chlorine occurs cleanly and efficiently on chromatographic alumina.