Synthesis of pyrimido[1,6-a]quinoxalines via intermolecular trapping of thermally generated acyl(quinoxalin-2-yl)ketenes by Schiff bases

Acyl(quinoxalin-2-yl)ketenes generated by thermal decarbonylation of 3-acylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones react regioselectively with Schiff bases under solvent-free conditions to form pyrimido[1,6-a]quinoxaline derivatives in good yields.

THEORETICAL STUDY ON THE UNIMOLECULAR REACTIONS OF GLYOXYLIC ACID

The potential energy surfaces of isomerization, decarboxylation, and decarbonylation reactions of glyoxylic acid have been characterized by the B3LYP/cc-pVTZ, B3LYP/aug-cc-pVTZ, and MP2/cc-pVTZ calculations. There is a relatively high barrier on the isomerization pathway from Tc to Tt , due to existence of the intramolecular H-bond in the Tc to Tt structures. The decarboxylation reaction proceeds mainly through a stepwise mechanism. The singlet hydroxyl carbene and carbon dioxide are formed in the first step, which is followed by isomerization of the carbene to formaldehyde in the second step. The thermal decarbonylation reaction of glyoxylic acid may take place at high temperature, due to a barrier of ~52 kcal/mol on the pathway.

Synthesis and Characterization of Supported Metal Cluster Catalysts with Well-Defined Structures

ABSTRACTNearly uniform supported metal clusters are the focus of this summary, which addresses their synthesis, characterization, and catalytic properties. Supported clusters represented as Ir4 and Ir6 were prepared on MgO powder by thermal decarbonylation of [HIr4(CO)11]− and [Ir6(CO)15]2−, respectively. The most useful characterization technique for supported clusters is extended X-ray absorption fine structure spectroscopy, but the structure data are limited by the precision of the coordination numbers (about ±20%). Ir4 and Ir6 clusters on supports catalyze hydrogenation of cyclohexene and of toluene, and they are catalytically distinct from larger iridium particles, although the reactions are structure insensitive (proceeding at about the same rate per exposed metal atom) when catalyzed by metal particles larger than about 1 nm. Thus the concept of structure insensitivity does not extend to supported metal clusters, which are regarded as quasi molecular.