Synthesis of 1,2-annulated and 1,2-unsubstituted pyrrolo[2,1,5-de]quinolizin-5-ones (cycl[3.3.2]azin-5-ones) via [3+2] cycloadditions of 1-oxoquinolizinium ylides with cyclic alkenes

Abstract

1,2-Annulated pyrrolo[2,1,5-de]quinolizin-5-ones (cycl[3.3.2]azin-5-ones) 6a-6k, 8a-8b and 9 have been synthesized by one pot tandem reactions of 2-acetyl-N-phenacylpyridinium bromides (1a-1d) with electron-deficient cyclic alkenes (N-alkyl(aryl)maleimides, benzoquinones and naphthoquinone) in the presence of sodium carbonate as a base and tetrakispyridinecobalt(II) dichromate (TPCD) as an oxidant. These products are formed by 1.3-dipolar cycloaddition of the 1-oxoquinolizinium ylides generated in situ from 1a-1d with the alkene followed by dehydrogenation of the primary cycloadduct under the action of TPCD. Similar reactions of the ylides generated in situ from 1a-1f with maleic anhydride gave the 1,2-unsubstituted pyrrolo[2,1,5-de]quinolizin-5-ones 7a-7f via oxidative bisdecarboxylation and dehydrogenation of the primary cycloadducts under the action of TPCD.

Cyclazines‐Structure and Aromaticity or Antiaromaticity on the Magnetic Criterion

“…N[2.2.3] has been early synthesized by Boekelheide and coworkers, [48,49] the UV‐Vis [7] and the proton NMR spectra [6] have been recorded and the aromaticity assigned; the effect of benzo‐annelation on the extent of aromaticity was a special topic and widely studied [4,5, 50−56] . Also various aza‐analogues of N[2.2.3] were classified accordingly (e. g. Figure S1–Supporting Information) [17,57–59] and the complex 1 H and 13 C NMR spectra completely assigned by Castle et al [60,61] .…”

“…As mentioned already, both N[2.3.3] − and N[2.3.3] + could not be synthesized yet, but especially the neutral 5‐thia analogue of cycl[3.3.2]azine N[2.3.3]S [and some aza‐derivatives] [70,72] have been intensively investigated [50,73–75] with the conclusions that proton chemical shifts around 4 to 6 ppm ( vide infra ) indicate a paratropic ring current in the peripheral 10c,12π system and anti‐aromaticity hereby; a substituted derivative of N[2.3.3]S has been synthesized [73] …”

“…The TSNMRSs of E have been calculated separately and included into Figure 3 [70,72] have been intensively investigated [50,[73][74][75] with the conclusions that proton chemical shifts around 4 to 6 ppm (vide infra) indicate a paratropic ring current in the peripheral 10c,12π system and anti-aromaticity hereby; a substituted derivative of N[2.3.3]S has been synthesized. [73] The TSNMRSs of 5-thia-cycl[3.…”

One‐Pot Synthesis of Pyrrolo[3,4‐a]indolizine‐1,3‐diones through [3+2] Cycloaddition‐Oxidation Reaction Catalyzed by CuII Salt and O2 as the Oxidant

“…Copper(II) salt is a particularly attractive oxidant because, under appropriate conditions and with suitable substrates, oxidation reactions can be carried out with catalytic amounts of Cu by using ambient air or O 2 as the stoichiometric oxidant 16. In continuation of our ongoing research interest in the synthesis of indolizine derivatives,14b,17 and with the aim of developing general and practical synthetic methods for polycyclic N‐heterocycles, we report the high‐yielding one‐pot synthesis of pyrrolo[3,4‐ a ]indolizine‐1,3‐diones from maleimides, pyridines, and acyl bromides through a [3+2] cyclization‐oxidation reaction catalyzed by Cu II salt by using molecular oxygen as the oxidant.…”

Exploration of N-hydroxy benzimidazole catalysts for hydrogen atom transfer reactions

“…The decarboxylation probably occurred via radical intermediates. 16 By changing the substrates from cyclic alkenes to non-cyclic dimethyl and diethyl maleate ( 3h and 3i ), the products were formed in yields of 54% and 55%, respectively, but further optimization of reaction conditions was required. This situation indicated that the cyclic structure of the alkene facilitated the cyclization step.…”