β-Selective C-H arylation of pyrroles leading to concise syntheses of lamellarins C and I.

The first general β-selective C-H arylation of pyrroles has been developed by using a rhodium catalyst. This C-H arylation reaction, which is retrosynthetically straightforward but results in unusual regioselectivity, could result in de novo syntheses of pyrrole-derived natural products and pharmaceuticals. As such, we have successfully synthesized polycyclic marine pyrrole alkaloids, lamellarins C and I, by using this β-selective arylation of pyrroles with aryl iodides (C-H/C-I coupling) and a new double C-H/C-H coupling as key steps.

Mechanistic studies on the Pd-catalyzed direct C-H arylation of 2-substituted thiophene derivatives with arylpalladium bipyridyl complexes.

Direct C-H phenylation of 2-ethylthiophene and 2-chlorothiophene with PhPdI(bipy) complex to form either the corresponding 4-phenyl or 5-phenylthiophene derivative is studied under stoichiometric conditions using various Lewis acids as additives. It is shown that reactions occur via the corresponding cationic Pd complex (PhPdbipy(+)) and that the counteranion determines the regioselectivity. High-level DFT calculations reveal that C-C bond formation occurs via a carbopalladation pathway and not via electrophilic palladation.

Programmed synthesis of tetraarylthiophenes through sequential C-H arylation.

A general protocol for the programmed synthesis of tetraarylthiophenes has been established. The utilization of three catalysts, RhCl(CO){P[OCH(CF(3))(2)](3)}(2), PdCl(2)/P[OCH(CF(3))(2)](3), and PdCl(2)/bipy, enables regioselective sequential arylations at the three C-H bonds of 3-methoxythiophene with iodoarenes. Interesting metal- and ligand-controlled regiodivergent C-H arylations have been uncovered during this study.

Potassium t-butoxide alone can promote the biaryl coupling of electron-deficient nitrogen heterocycles and haloarenes.

The biaryl coupling of electron-deficient nitrogen heterocycles and haloarenes can be promoted by potassium t-butoxide alone, without the addition of any exogenous transition metal species. Electron-deficient nitrogen heterocycles such as pyridine, pyridazine, pyrimidine, pyrazine, and quinoxaline are arylated with haloarenes. Control experiments support a radical-based mechanism.