Orthogonal and auto-tandem catalysis: synthesis of dipyrido[1,2-a:2',3'-d]imidazole and its benzo and aza analogues via inter- and intramolecular C-N bond formation.

[reaction: see text] The synthesis of dipyrido[1,2-a:2',3'-d]imidazole and hitherto unknown benzo and aza analogues is described. These relatively complex polycyclic heterocycles could be smoothly prepared in one step from commercially available building blocks. Mechanistically, the developed procedure involves orthogonal (Pd and Cu catalyst) or auto-tandem (Pd catalyst) catalysis via regioselective inter- and intramolecular C-N bond formation.

The first tandem double palladium-catalyzed aminations: synthesis of dipyrido[1,2-a:3',2'-d]imidazole and its benzo- and aza-analogues.

A new strategy for the synthesis of the title compounds via a regio- and chemoselective one-pot inter- and intramolecular Buchwald-Hartwig amination of 2-chloro-3-iodopyridine with aminoazines and -diazines is reported.

Study of a new rate increasing "base effect" in the palladium-catalyzed amination of aryl iodides.

Evidence for an interphase deprotonation of Pd(II)-amine complexes with weak carbonate base has been gained for the first time. When a rate-limiting deprotonation step is involved in the catalytic cycle, controlling the structure (shape and size of the particles) and/or molar excess of the carbonate base used can significantly increase the reaction rate of Buchwald-Hartwig aminations. By taking such a "base effect" into account a general protocol for the intermolecular amination of aryl iodides with all types of amines has been developed based on a standard Pd-BINAP catalyst, using cesium carbonate as the base.

Fragmentation study of diastereoisomeric 2-methyltetrols, oxidation products of isoprene, as their trimethylsilyl ethers, using gas chromatography/ion trap mass spectrometry.

The diastereoisomeric 2-methyltetrols, 2-methylthreitol and 2-methylerythritol, were recently reported as major secondary aerosol components in natural forest aerosols and proposed as molecular markers for the photooxidation of isoprene. In this study, we examine the complex electron and methane chemical ionization behaviors of their trimethylsilyl ethers. In order to gain insight into their fragmentation behaviors, threitol and erythritol were studied as model compounds, and deuterium labeling of the trimethylsilyl groups and ion trap MS2 experiments were performed.