One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation.

Ji Ma,Junzhi Liu,Xinliang Feng,Yubin Fu

doi:10.3762/bjoc.16.72

Ji Ma, Junzhi Liu + Show 2 more

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https://doi.org/10.3762/bjoc.16.72

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Abstract

A novel dicyclopenta-fused peropyrene derivative 1 was synthesized via a palladium-catalyzed four-fold alkyne annulation of 1,3,6,8-tetrabromo-2,7-diphenylpyrene (5) with diphenylacetylene. The annulative π-extension reaction toward 1 involved a twofold [3 + 2] cyclopentannulation and subsequent twofold [4 + 2] benzannulation. The structure of 1 is unambiguously confirmed by X-ray crystallography; 1 adopted a twisted geometry due to the steric hindrance of the phenyl rings and the hydrogen substituents at the bay regions. Notably, compound 1 exhibits a narrow energy gap (1.78 eV) and a lower LUMO energy level than the parent peropyrene without the fusion of the five-membered rings. In addition, the effects of the peri-fused pentagons on the aromaticity and molecular orbitals of 1 were evaluated by theoretical calculations. This work presents an efficient method to develop π-extended aromatic hydrocarbons with cyclopenta moieties.

Highlights

Significant efforts have been recently devoted to the synthesis of nonalternant cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs), which represent the topological subunits of fullerenes and exhibit high chemical, physical and biological activities [1,2,3,4,5,6,7,8,9,10]
In order to gain a deeper insight into the effects of the fused 5-membered rings on the peropyrene core, the electronic structures and the frontier orbitals of the peropyrene derivative 6 without pentagons and of compound 1 are compared by DFT calculations at the B3LYP/6-311++G(d,p) level
We demonstrated the first synthesis and characterization of a dicyclopenta-fused peropyrene 1 starting from pyrene in four steps in which the twofold pentannulation and subsequent twofold benzannulation based on 1,3,6,8-tetrabromo-2,7-diphenylpyrene is the key step

Summary

Introduction

Significant efforts have been recently devoted to the synthesis of nonalternant cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs), which represent the topological subunits of fullerenes and exhibit high chemical, physical and biological activities [1,2,3,4,5,6,7,8,9,10]. The reported synthetic methods towards the (di-)cyclopenta-fused pyrene congeners (i–iii, Scheme 1) have mainly been reliant on the flash vacuum pyrolysis of suitable precursors under harsh conditions (T ≥ 900 °C), which resulted in relatively low yields While aiming at the synthesis of the novel tetracyclopenta-fused pyrene derivative 2 through the quadruple annulation of 1,3,6,8-tetrabromo-2,7-diphenylpyrene (5) with 1,2diphenylethyne, an unprecedent dicyclopenta-fused peropyrene congener 1 was obtained (Scheme 2).

Results

Conclusion