Novel 2-phenyl-6,11- and 2-phenyl-4,9-methanocycloundecapyrroles (15a and 16a) were synthesized in moderate yields by the reaction of 3,8-methanoannulenone (3), a 10π-electron vinylogue of tropone, with [(1-phenylvinyl)imino] triphenylphosphorane (8a) and subsequent dehydrogenation. Similarly, the reaction of the annulenone 3 with (inden-3-ylimino)tributylphosphorane (8c) and subsequent aromatization afforded 7,12- and 9,14-methano-15H-cycloundeca[b]indeno[2,3-d]pyrroles (15c and 16c), which also have methanocycloundeca[b]pyrrole ring systems. Preparation of 2-phenyl-5,10-methanocycloundeca[b]pyrrole (17), an isomer of both 15a and 16a, was also accomplished in low yield by the reaction of 4,9-methano annulenone (5) with an excess of [(1-phenylvinyl)imino]tributylphosphorane (8d). The reactivity of annulenone 5 with (vinylimino) phosphoranes was found to be quite low as compared to the higher reactivity of annulenone 3 and tropone. Compounds 15a,c, 16a,c, and 17 are the first nitrogen analogues of cyclopentacycloundecene ring systems which have vinylogous structures of 1-azaazulene. Structures of the products obtained were examined by 1H NMR spectra and UV spectra. The 1H NMR spectra clarified that the compounds 15a,c, 16a,c, and 17 are aromatic molecules having a diatropic 14π-electron system, and 5,10-methano derivative 17 has a more diatropic nature than the compounds 15a,c and 16a,c. The UV spectra of 15a,c, 16a,c, and 17 exhibited increased cyclic conjugation of the aromatic perimeter according to a bathochromic shift of the longest absorption maxima as compared to the corresponding 1-azaazulene derivatives.
ASJC Scopus subject areas
- Organic Chemistry