NMR and DFT studies on persistent carbocations derived from benzo[kl ]xanthene, dibenzo[d ,d ′]benzo[1,2-b :4,3-b ′]difuran, and dibenzo[d ,d ′]benzo[1,2-b :4,5-b ′]difuran in superacidic media

Abstract

Persistent carbocations generated by the protonation of hetero‐polycyclic aromatic compounds with oxygen atom(s) were studied by experimental NMR and density function theory calculations. Benzo[kl]xanthene (1), dibenzo[d,d′]benzo[1,2‐b:4,3‐b′]difuran (2), and dibenzo[d,d′]benzo[1,2‐b:4,5‐b′]difuran (3) were synthesized by the annulation of arenediazonium salts. Compound 1 in FSO3H‐SbF5 (4:1)/SO2ClF and 3 in FSO3H‐SbF5 (1:1)/SO2ClF ionized to 1aH+ with protonation at C(4) and to 3aH+ with protonation at C(6), and these cations were successfully observed by NMR at low temperatures. The density function theory calculations indicated that 1aH+ and 3aH+ were the most stable protonated carbocations and that 2 should ionize to 2aH+ with protonation at C(6). According to the changes in 13C chemical shifts (Δδ13C), the positive charge was delocalized into the naphthalene unit for 1aH+, into one benzo[b,d]furan unit for 2aH+, and into one benzo[b,d]furan unit for 3aH+. Copyright © 2015 John Wiley & Sons, Ltd.

Phenanthrene cyclocarbonylation – core post-synthetic modification of phenanthriporphyrin

“…Alternatively, these species can be treated as macrocyclic carbocations, which tend to reveal distinct 1 H NMR patterns due to localization of the positive charge at selected positions (Scheme 8B). 52–56 The hypothetical open-chain derivative 9-H 2 2+ containing the 3,6-bis(( Z )-(2 H -pyrrol-2-ylidene)methyl)phenanthrene unit formally formed by extrusion of 16-benzyl from 7-H 2 2+ (Scheme 8C) is included for the sake of comparison.…”

Catalyst‐Free Synthesis of O‐Heteroacenes by Ladderization of Fluorinated Oligophenylenes

“…Despite a large number of works aimed to develop facile incorporation of the furan ring, the principal synthetic strategies are not so numerous and break down into few categories depicted in Figure 1. The final step includes either transition metal‐catalyzed C−C coupling [22–26] or C−O bond creation, [17, 27–35] which is usually implemented via a two‐step deprotection/dehydration procedure [10, 14, , 18, 36–38] …”

Catalyst‐Free Synthesis of O‐Heteroacenes by Ladderization of Fluorinated Oligophenylenes

“…Despite a large number of works aimed to develop facile incorporation of the furan ring, the principal synthetic strategies are not so numerous and break down into few categories depicted in Figure 1. The final step includes either transition metal-catalyzed CÀC coupling [22][23][24][25][26] or CÀO bond creation, [17,[27][28][29][30][31][32][33][34][35] which is usually implemented via a two-step deprotection/dehydration procedure. [10, 14, , 18, 36-38] With rare exceptions, [39] the existing synthetic approaches to the dibenzofuran core require an oxygen atom in the precursors structure.…”