Two‐Dimensional Acetylenic Scaffolding: Extended Donor‐Substituted Perethynylated Dehydroannulenes

Abstract

Starting from (Z)-bis(N,N-diisopropylanilino)-substituted tetraethynylethene (TEE), perethynylated octadehydro[12]- and dodecadehydro[18]annulenes were prepared by oxidative Hay coupling. The dodecadehydro[18]annulene with six peripheral N,N-diisopropylanilino substituents was characterized by X-ray crystallography. Elongation of the Z-bisdeprotected TEE by Cadiot-Chodkiewicz coupling with 1-bromo-2-(triisopropylsilyl)ethyne provided a Z-configured bis(butadiyne), which after alkyne deprotection afforded under Hay coupling conditions N,N-diisopropylanilino-substituted perethynylated hexadecadehydro[20]- and tetracosadehydro[30]annulenes. The diisopropylanilino substituents enhance the properties of these unprecedented all-carbon perimeters in several distinct ways. They ensure their solubility, increase their stability, and importantly, engage in strong intramolecular charge-transfer interactions with the electron-accepting all-carbon cores, resulting in intense, bathochromically shifted charge-transfer bands in the UV/Vis spectra. The charge-transfer character of these bands was confirmed by protonation-neutralization experiments. The redox properties of the new carbon-rich chromophores were investigated by cyclic voltammetry and rotating disk voltammetry, which indicated different redox behavior for aromatic (4n+2 pi electrons) and antiaromatic (4n pi electrons) dehydroannulenes.

Expedient Synthesis of Functionalized Conjugated Enynes: Palladium‐Catalyzed Bromoalkynylation of Alkynes

“…Importantly, silylethynyl bromides have proven to be useful starting materials for the construction of conjugated enynes. [6] To our surprise, the use of 1,4-bis(2-bromoethynyl)benzene resulted in the formation of the corresponding product 3 la in 79 % yield in one step.…”

“…In the presence of the Pd(OAc) 2 catalyst (5 mol %), the reaction of phenylethynyl bromide (1 a, 1.2 mmol) and 4-octyne (2 a, 1 mmol) in THF at 30 8C afforded 3 aa in a 30 % yield (entry 1). The screening of various solvents revealed that the solvent played a very important role in this reaction (entries [1][2][3][4][5][6]. Only trace amounts of the desired product 3 aa was obtained when DMSO was used (entry 2), and unsatisfactory results were obtained using toluene (entry 4).…”

All‐Carbon Scaffolds by Rational Design

“…Figure 2 shows some of the perethynylated dehydroannulene perimeters together with their longest-wavelength absorption maxima and the first oxidation and reduction potentials obtained by cyclic voltammetry (CV) and rotating-disk voltammetry (RDV). [84][85][86][87][88][89] If not indicated otherwise, all electrochemical potentials reported in this Review were recorded in CH 2 Cl 2 (þ0.1 M n-Bu 4 NPF 6 ) and referenced against the ferricinium/ ferrocene (Fc þ /Fc) couple as internal standard. The chargetransfer character of the longest-wavelength absorption maximum in the UV-vis spectra of donor-acceptor systems was confirmed by protonation (disappearance of the band) and reneutralization (reappearance of the band).…”

Donor- and/or Acceptor-Substituted Expanded Radialenes: Theory, Synthesis, and Properties

“…The product was cross-coupled to 4-iodobenzonitrile (0.060 g, 0.26 mmol) in deoxygenated THF (5 mL) in the presence of Pd(PPh 3 ) 4 (0.008 g, 0.007 mmol), iPr 2 NH (2 mL), and CuI (0.0025 g, 0.013 mmol) at 40−50°C for 18 h. The reaction was cooled to rt, Et 2 O (10 mL) and H 2 O (5 mL) were added, the organic phase was separated, washed with saturated aq NH 4 Cl (2 × 50 mL) and brine (2 × 50 mL), dried (MgSO 4 ), and filtered, and the solvent was removed in vacuo. Flash column chromatography (silica gel CH 2 Cl 2 /hexanes 3:10 → 1:1) followed by precipitation from hexanes afforded compound 27 (0.091 g, 57% from 13) as a yellow solid: mp 114−116°C (discolors, dec); R f = 0.37 (EtOAc/hexanes 3:17); UV−vis (CH 2 Cl 2 ) λ max (ε) 448 (30900), 332 (63400), 250 (49600) 20) provided the crude terminal diyne (ca. 0.08 g, ca.…”