On the Reaction of (Vinylimino)phosphoranes and Related Compounds. 20. Syntheses and Properties of Methanocyclodeca[b]pyridine Ring Systems

Novel 2-[(triphenyl- and 2-[(tributylphosphoranylidene)amino]-1,6-methano[10]annulenes (8x,y) and 3-[ (triphenyl- and 3-[(tributylphosphoranylidene)amino]-1,6-methano[10]annulenes (9x,y) were generated by the Staudinger reaction of 2- and 3-azido-1,6-methano[10]annulenes (5 and 6). The compound 8x was inert to α,β-unsaturated ketones, while compounds 8y and 9y were found to react with α,β-unsaturated ketones in enamine-alkylation process followed by aza-Wittig reaction and dehydrogenation to give 7,12- and 5,10- methanocyclodeca [b] pyridines 20a-f and 26a,f, respectively. The reactivity of 8 and 9 as well as the site selectivity of 9 was suggested by their ¹³C NMR spectra, in which the carbon signals of the nucleophilic center appear at higher field as compared to those of 1,6-methano[10]annulene. Structural properties of 20a-f and 26a,f were examined by ¹H NMR and UV spectra. The ¹H NMR spectra analyzing aromatic characters clarified both remarkable reduction of a ring current and appearance of bond alternation as compared to the parent 1,6-methano [10]annulene (1). The UV spectra exhibiting a prolonged cyclic conjugation are in contrast to their 10π electron analogues, 1,6-methano[10]annulene (1) and quinoline derivatives.