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

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.


General methods and materials
All reagents were purchased from commercial suppliers and used as received without further purification. The 1 H NMR and 13 C NMR spectra were recorded in deuterated solvents on a Bruker DPX 300 or an AV-III 600 NMR spectrometer. Chemical shifts are given in ppm relative to tetramethylsilane (TMS), coupling constants J are given in Hertz, the solvent signals were used as reference. Coupling constants were determined assuming first-order spin-spin coupling.
Preparative recycling gel permeation chromatography (r-GPC) was performed with a JAI LC-91XX II NEXT instrument equipped with JAIGEL-1H/JAIGEL-2H columns using chloroform as an eluent. High-performance liquid chromatography (HPLC) was performed with a Shimadzu HPLC instrument equipped with a silica column using toluene/hexane (1:3) as an eluent. UV-visible (UV) spectra were measured on an Agilent Cary 5000 UV-VIS-NIR spectrophotometer by using a 10 mm optical path quartz cell at room temperature. Cyclic voltammetry (CV) measurements were carried out on a CHI 760 E potentiostat (CH Instruments, USA) in a three-electrode cell in a dichloromethane solution of Bu4NPF6 (0.1 M) with a scan rate of 50 mV/s at room temperature. A Pt wire, Ag/AgCl (3 M KCl solution), and a glassy carbon electrode were used as the counter electrode, the reference electrode, and the working electrode, respectively.

Detailed synthetic procedure and characterization data
Scheme S1.

2,7-Diphenylpyrene (4)
The synthetic procedure for 4 is in a similar manner as described in ref. [2]. To a solution of compound 3 (2.0 g, 4.40 mmol) and the corresponding bromobenzene (4.6 mL, 44.0 mmol) S4 dissolved in toluene (60 mL) was added a 2 M solution of sodium carbonate (2.3 g, 22.0 mmol) dissolved in water (10 mL). The mixture was bubbled with Argon for 30 min. Then, tetrakis(triphenylphosphine)palladium(0) (508 mg, 0.44 mmol) and phase-transfer agent Aliquat 336 (5 drops) were added. The mixture was heated to 90 °C for 48 h under argon atmosphere. The resulting mixture was cooled to room temperature, most of the solution was removed by rotavapor and then poured into methanol (300 mL). The resulting precipitate was filtered off, washed with water, dilute acid (5% HCl), water, methanol, then with acetone to remove the starting material as well as the mono-substituted by-product. After drying in vacuum, compound 4 is obtained as a white solid (1.2 g, 77%). 1
The mixture was kept at 120 °C for 5 h and then cooled to room temperature. The cooled reaction solution was poured into methanol (150 mL) and the precipitate filtered off. Further drying of the precipitate in high vacuum gave the crude product. Then it was purified by recrystallization from chloroform to obtain the title compound in a yield of 86% (320 mg). 1

Proposed pathway of the annulation reaction towards 1
Scheme S2. Possible pathway to the formation of 1 from the precursor 5.

X-ray crystallographic analysis of 1
Single crystals of 1 were obtained by slowly evaporation from a carbon disulfide solution. The X-ray crystallographic coordinates for structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition number CCDC 1984017 (1). These data can be obtained free of charge from CCDC via http://www.ccdc.cam.ac.uk/data_request/cif

Details of the theoretical calculations
All density functional theory (DFT) calculations were performed using the Gaussian 09 program [4]. The B3LYP functional was used for geometry optimization in the ground state.
The 6-311+G(2d, p) basis set was used for the C and H atoms. All the geometry optimization was done in the gas phase and based on the single crystal structure. Nucleus independent chemical shifts (NICS) values were calculated using the standard gauge invariant atomic orbital (GIAO) [5] method at B3LYP functional.         Figure S15. MALDI-TOF mass spectrum of compound 3. S15 Figure S16. MALDI-TOF mass spectrum of compound 4. Figure S17. MALDI-TOF mass spectrum of compound 5.