A New Route to the Acepleiadylene System

The road to bis‐periazulene (cyclohepta[def]fluorene): Realizing one of the long‐standing dreams in nonalternant hydrocarbons

“…[62] (C) Cycloadditions of 19 to the multiple substituted derivatives of 36. [63] (D) Wang et al's facile synthetic route for 36 and further π extensions. [64] Cyclohepta[bc]acenaphthylene 37 was reported in 1955 by Reid et al [70] They synthesized 37 from the butyric acid derivative in three steps and isolated it as a dark red crystalline solid (Figure 9B).…”

“…[ 62 ] Afterward, Prinzbach's group established the synthesis of the dicyano‐substituted derivatives of 36 through cycloadditions of their own cyclohepta[ e ]indene derivative 19 with various olefins or acetylenes, such as piperidines, dimethyl acetylenedicarboxylate, maleic anhydride, and quinones (Figure 8C). [ 63 ] Very recently, a dramatically improved synthetic route was reported by Wang et al [ 64 ] They employed a double Suzuki‐type coupling with 5,6‐dibromoacenaphthene to construct a new seven‐membered ring and a streamlined dehydrogenation condition using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) in the presence of t BuOK, to give 36 in 44% in two steps (Figure 8D). The same group demonstrated further π extensions of 36 to nanographene‐type molecules having the nonalternant scaffold(s).…”

“…[ 62 ] (C) Cycloadditions of 19 to the multiple substituted derivatives of 36 . [ 63 ] (D) Wang et al's facile synthetic route for 36 and further π extensions. [ 64 ]…”

Non‐Alternant Non‐Benzenoid Aromatic Compounds: Past, Present, and Future

“…For the 5‐6‐7 (14 π‐electron) system, the linearly fused cyclohepta[ f ]indene ( 6 ) is unknown . For angularly fused cyclohepta[ e ]indene ( 7a , also called “phenazulene”), the parent hydrocarbon turned out to be unstable and survived for only several hours at −60°C; only its derivatives 7b and 7c bearing cyano groups were isolated . No attempts seem to have been made to prepare the 7‐6‐7 (16 π‐electron) ring conjugated systems 8 and 9 .…”

Synthesis of New Hydroxybenzo[a]carbazoles

“…The proposed mechanism leading to the formation of compound 8 is outlined in Scheme 3. After demethylation of compound 7 and oxidation to the quinone, a second molecule of DDQ could give rise to a Diels-Alder reaction 12,13 leading to intermediate 7a. Then, after oxidation to 7b, a retro-Diels-Alder reaction could lead to compound 8.…”