Oxidative Cyclodimerization After Tandem Cyclization of Dehydrobenzo[14]annulenes Induced by Alkyllithium

Abstract

Highly ethynylated compounds have the potential to be transformed into polycyclic aromatic hydrocarbons by intramolecular cyclizations between the sp-carbon atoms because of the high reactivity of carbon-carbon triple bonds. [1] Particularly those with cyclic structures are useful for the construction of new carbon frameworks which are otherwise difficult to obtain. Moreover, cyclic precursors would limit the number of possible reaction pathways because of steric constraints. Indeed, a few examples of efficient transformations of dehydrobenzannulenes into polycyclic carbon frameworks were reported as exemplified for octadehydrodibenzo [12]annulene, [2] hexadehydrotribenzo [12]annulene, [3] and tetradehydrodibenzo [8]annulene.[4] The reactions are typically induced by attack of a nucleophile, [4a] an electrophile, [2, 4b] or a radical, [3c] or initiated by reduction to generate a radical anion. [3a,b] We envisaged that octadehydrotribenzo [14]annulene ([14]DBA) 1 a [5] and its congeners 2-4 would serve as intriguing substrates for multiple trasnannular bond formations to yield new polycyclic frameworks because of the presence of four closely located triple bonds. Additionally, the distorted butadiyne unit is expected to trigger reactions induced by an electrophile [2a] or a nucleophile, [4a] which would not occur for unactivated acetylenic bonds. [4a, 6] We report herein the results of the reactions of 1 and its congeners, 2-4, with butyllithium (nBuLi). We discovered an unprecedented oxidative cyclodimerization to form eight-membered ring products, in which two indeno[2,1-a]fluorene components are connected by a single and a double bond, following three transannular CÀC bond formations.First we envisioned the possible pathways for the tandem transannular cyclizations of 1 a as shown in Scheme 1. In the initial step, we assume the formation of a five-membered ring after the addition of a nucleophile to the diyne moiety of 1 a to give the intermediate 7 on the basis of the previous reports. [2a, 3, 4a] For the second step, there are two options of transannular bond formation: 1) formation of a four-membered ring to give 9 or 2) a five-membered ring to form the 5/ 8/5 ring system 8. In the former case, the resulting ninemembered ring can be further divided into 5/6 a ring system to afford the tetracyclic intermediate 11 bearing an indeno[2,1-a]fluorene substructure, or the 4/7 system 10 possessing two benzocyclobutene units. As to the indeno[2,1-a]fluorene framework, while Le Berre et al. reported the synthesis of the unstable 11,12-diphenylderivatives 5 a, [7] we succeeded recently in the synthesis of the robust dimesityl-substituted derivative 5 b and clarified its physical properties including its singlet diradical character.[8] These results suggest that the expected product 12, formed by interception of 11 with an electrophile, must be substantially reactive.When the di-tert-butyl[14]DBA 1 b was treated with nBuLi at À78 8C in THF and subsequently quenched with water or 1-iodobutane at the same tem...

On-Surface Synthesis of Antiaromatic and Open-Shell Indeno[2,1-b]fluorene Polymers and Their Lateral Fusion into Porous Ribbons

“…This interchain fusion generates ribbons (referred to as 6 , see nc-AFM image in Figure b) made of tetraindenopyrene repeating units and hosting uniform pores with a rim composed of 16 carbon atoms. The polymers preferentially couple with the five-membered rings facing each other, as also observed for indeno­[2,1- a ]­fluorene derivatives in solution. , The average length of 6 is 10 nm, with a maximum observed length of 30 nm. Around 21% of the molecular units (out of more than 3000) form the ribbons 6 , while the rest remains in chains of type 3 .…”

Indenofluorene congeners: Biradicaloids and beyond

“…Though Le Berre reported the synthesis of 11,12-diphenylindenofluorene 3c, its molecular structure and detailed electronic structure have not been investigated [15]. We initiated our research in the indenofluorene field inspired by an accidental finding of a dimeric product 14, which is most likely formed via an intermediate 13 having an indenofluorene backbone, obtained by treatment of octadehydrotribenz [14] annulene (12) with n-butyllithium (Scheme 2) [21]. This finding prompted us to investigate molecular and electronic structure of stabilized dimesityl derivative of indeno[2,1-a]fluorene 3b as described below [16].…”

π‐Conjugated Macrocycles Bearing Angle‐Strained Alkynes

“…− These macrocycles are similar to 89 a with strained monoynes and a diyne. Because of its stability and planarity, Haley, Tobe, Hisaki and Miyata, and other research groups independently explored the synthesis of related dehydrobenzo[14]annulenes, their transformation, and their applications as fluorescent materials and in supramolecular assemblies . [16]DBA 90 (DBA=dehydrobenzoannulene) was synthesized by Haley and co‐workers .…”

“…Because of its stability and planarity,H aley,T obe, Hisaki and Miyata, and other research groups independently explored the synthesis of relatedd ehydrobenzo [14]annulenes,t heir transformation, and their applications as fluorescent materials and in supramolecular assemblies. [142,[163][164][165][166][167][168][169][170][171] [16]DBA 90 (DBA = dehydrobenzoannulene) was synthesized by Haley and co-workers. [159,172,173] X-ray analysisr evealed that the diyne moiety is slightly strained.…”