MESO-SUBSTITUTION REACTION OF ZINC OCTAETHYLPORPHYRIN VIA ANODIC OXIDATION

meso-Nitration, chlorination and acetoxylation of ZnOEP viaanodic oxidation are reported to proceed via EE'C, ECE and EE'C mechanismrespectively.     

Semilinear elliptic problems in annular domains

The method of shooting is used to establish existence of positive radially symmetric solutions to nonlinear elliptic equations of the form u+f(r, u)=0 on annular regionsa<r=|x|<b inR ^N , satisfying Dirichlet or Neumann conditions on the boundary. This extends recent work done by Bandle, Coffman and Marcus. A result concerning uniqueness of such solutions is also extended.

---

Zusammenfassung Mit Hilfe eines Schiessverfahrens wird die Existenz von Lösungen nichtlinearer Probleme der Form u+f(r, u)=0 in ringförmigen Gebieten nachgewiesen, die verschiedenen Randbedingungen genügen. Es wird auch ihre Eindeutigkeit untersucht. Diese Arbeit verallgemeinert gewisse Ergebnisse von Bandle, Coffman und Marcus.

---

Résumé On utilise une méthode de tir pour établir l'existence de solutions de problèmes non linéaires du type u+f(r, u)=0 dans des anneaux, vérifiant différentes conditions aux limites. Ensuite on discute l'unicité de ces solutions. Ce travail généralise certains résultats de Bandle, Coffman et Marcus.

---

---

This work was supported by the Applied Mathematical Sciences subprogram of the Office of Energy Research, U.S. Department of Energy, under contract W-31-109-Eng-38. The author also wants to thank the Mathematics Institute, University of Basel, for supporting a visit in Oct., 1987 during which the project was initiated.     

Regio- and enantioselective intermolecular rhodium-catalyzed [2+2+2] carbocyclization reactions of 1,6-enynes with methyl arylpropiolates

Transition metal-catalyzed [m+n+o] carbocyclization reactions provide powerful methods for the construction of complex polycyclic systems that are generally not accessible through classical pericyclic reactions. We have developed the first regio- and enantioselective crossed intermolecular rhodium-catalyzed [2+2+2] carbocyclization of carbon- and heteroatom-tethered 1,6-enynes with unsymmetrical 1,2-disubstituted alkynes. This study clearly delineates the ligand requirements for obtaining excellent regio- and enantioselectivity. Furthermore, the ability to utilize various electron-withdrawing groups, and to introduce quaternary carbon stereogenic centers, provides the level of versatility necessary for its application to target-directed synthesis. Additional studies on the development and application of this novel methodology to the total synthesis of natural products are currently underway.     

Rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction

An interesting rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction was developed. A chiral atropisomeric dipyridyldiphosphane ligand was found to be highly effective in this system. This operationally simple protocol allows both catalyst and reactants to be handled under air without precautions. Various enynes were transformed to the corresponding bicyclic cyclopentenones in good yield and enantiomeric excess (up to 95 % ee). A study of the electronic effects of the enyne substrates revealed a correlation between the electronic properties of the substrates and the ee value obtained in the product of the Pauson-Khand-type reaction. A linear free-energy relationship was observed from a Hammett study.     

ZnO hierarchical structures for efficient quasi-solid dye-sensitized solar cells

We report a direct precipitation method for mass production of ZnO microflowers (MFs) containing hierarchical structures. The ZnO MFs are constructed by interlaced single crystalline and porous nanosheets which are ideal photoanode material for dye-sensitized solar cells (DSCs) because the MFs can largely improve the energy harvesting performance and the efficiency of DSCs. Compared with other forms of nano-sized structures, the novel hierarchical structures show obvious advantages in DSC application because of their large surface area for dye-loading, good light scattering efficiency and excellent electrical transport property. The quasi-solid state DSCs fabricated with the MF hierarchical structures exhibited an efficiency of 4.12%, much higher than that of ZnO nanoparticle-based DSCs, indicating a great potential for the development of highly-efficient quasi-solid DSCs.