Covalent tethering of organic functionality to the surface of glassy carbon electrodes by using electrochemical and solid-phase synthesis methodologies

Organic linkers such as (N-Boc-aminomethyl)phenyl (BocNHCH2C6H4) and N-Boc-ethylenediamine (Boc-EDA) have been covalently tethered onto a glassy carbon surface by employing electrochemical reduction of BocNHCH2C6H4 diazonium salt or oxidation of Boc-EDA. After removal of the Boc group, anthraquinone as a redox model was attached to the linker by a solid-phase coupling reaction. Grafting of anthraquinone to electrodes bearing a second spacer such as 4-(N-Boc-aminomethyl)benzoic acid or N-Boc-beta-alanine was also performed by following this methodology. The surface coverage, stability and electron transfer to/from the tethered anthraquinone redox group through the linkers were investigated by cyclic voltammetry. The effects of pH and scan rate were studied, and the electron-transfer coefficient and rate constant were determined by using Laviron's equation for the different types of linker. The combination of electrochemical attachment of protected linkers and subsequent modifications under the conditions of solid-phase synthesis provides a very versatile methodology for tailoring a wide range of organic functional arrangements on a glassy carbon surface.     

First Stereoselective Total Synthesis of a Dimeric Naphthoquinonopyrano‐γ‐lactone: (+)‐γ‐Actinorhodin

We have accomplished the first total synthesis of an isomerically pure naphthoquinonopyrano‐γ‐lactone dimer, γ‐actinorhodin, in eleven steps. Two steps exploit pairs of peri‐MeO groups as unusual selectivity controls. The respective MeO groups convey the steric bulk of a bromo or iodo substituent located ortho to one MeO group as steric hindrance into the vicinity of the second MeO group. This relay effect was indispensable for exerting regiocontrol in an aromatic bromination and diastereocontrol in an oxa‐Pictet–Spengler cyclization. The absolute configuration of our target compound was established in an asymmetric Sharpless dihydroxylation of a β,γ‐unsaturated ester, which was synthesized in a Heck coupling of a bromoiodonaphthalene with ethyl vinylacetate. The dihydroxylation provided the γ‐hydroxylactone moiety of the bromonaphthalene that was used as the substrate in the oxa‐Pictet–Spengler cyclization. Dimerization to the core of γ‐actinorhodin occurred by two Suzuki couplings.     

Syntheses, properties, and photoreactions of the hybrid molecules consisting of a Co(II) mononuclear complex and porphyrins

New hybrid molecules consisting of mononuclear Co(II) complexes and porphyrin moieties were synthesized and their new photoreactions were examined. Three porphyrins with different meso-substituents (2,6-dimethoxyphenyl, 3,5-di-tert-butylphenyl, and 2,6-difluorophenyl groups) were used to change the redox potentials of the hybrid compounds. The hybrid molecules were prepared by the stepwise condensation of amide bonds. The cyclic voltammograms of these hybrid molecules showed the redox processes of both the cobalt and porphyrin moieties. The redox potentials of the porphyrins showed a systematic change that was consistent with the electronic effects of the meso-substituents. The emission spectra only showed fluorescence of the porphyrins with slightly decreased intensities. When a solution of the hybrid molecule, durohydroquinone, and N,N-diisopropylethylamine in CHCl(3)/MeCN was irradiated with visible light (>580 nm), durohydroquinone was converted into duroquinone with the concurrent formation of the reduced product of CHCl(3). The hydroquinone was employed as an electron donor capable of reversible redox reactions, which is in contrast to conventional sacrificial reagents such as EDTA. The course of the photoreaction was followed by (1)H NMR spectroscopy and the amount of produced duroquinone was between 50-60% after 600 min. We propose that the photoreaction involves a photoinduced electron transfer from the hydroquinone to the excited porphyrin, followed by the formation of a Co(I) intermediate by charge shift, thus leading to the reaction with CHCl(3).     

Electronic Structures and Chiroptical Properties of Post‐functionalized Helicene Quinones

The synthesis of redox‐active p‐ and o‐quinones 2‐phenylamino‐4‐phenylimino[6]helicene‐1‐one 1 , 2‐phenylamino[6]‐helicene‐1,4‐dione 2 , and 4‐phenyl[6]helicene‐1,2‐dione 3 in their enantiopure forms by post‐functionalization of (P)‐ and (M)‐1,2‐dimethoxy[6]helicene is presented. Structural characterization in solution and in the solid state was accomplished by 2D NMR spectroscopy methods and X‐ray diffraction analysis, respectively. Interpretation of electrochemical redox data was accompanied by a detailed orbital picture, derived from DFT calculations. The electronic structures of compounds 1 – 3 were investigated by UV/Vis and electronic circular dichroism (ECD) spectroscopy, complemented by TD‐DFT calculations. Quinones 1 – 3 were chemically reduced to study the EPR signatures of their respective radical anions. DFT methods were used for the atom assignment of the hyperfine coupling constants. The results are discussed within the context of electrochromic chiral switches and molecular recognition.     

Reaction of benzoquinones and naphthoquinones with 1,8-diamino-3,6-dioxanonane and with 1,11-diamino-3,6,9-trioxaundecane

Reaction of 1,4-naphthoquinone or 2,3-dichloro-1,4-naphthoquinone with α,ω-diamino-derivatives of poly(alkylenoxides) leads to the formation of α,ω-bis(quinonyl) amines. A similar reaction with chloranil, bromanil, dichlorodicyanobenzoquinone, S-phenylbenzoquinone and 1,4-benzoquinone itself, leads to the formation of quinoid crown ethers.     

Oxidation of triphenylantimony with 4-hydroperoxy-2-hydroxy-3,4,6-triisopropylcyclohexa-2,5-dienone or 3,4,6-triisopropyl-1,2-benzoquinone

According to the NMR spectroscopic data, the oxidation of triphenylantimony with 4-hydroperoxy-2-hydroxy-3,4,6-triisopropylcyclohexa-2,5-dienone involves three steps. The first step affords the 2,4,10,12-tetraoxa-3,11-distibatricyclo[11.3.1.1^5,9]octadecatetraene derivative. The latter is rearranged into benzodioxastibolone derivatives followed by the rearrangement into 4,6,7-triisopropyl-2,2,2-triphenyl-1,3,2-benzodioxastibol-5-ol. The transformation of the latter depends on the presence of oxygen and the mode of its dosing. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1750–1757, September, 2007.