Metal-catalyzed coupling/carbonylative cyclizations for accessing dibenzodiazepinones: an expedient route to clozapine and other drugs

A sequential strategy to access 10,11-dihydro-5H-dibenzo[b,e][1,4]diazepinones (DBDAPs) is disclosed in this article through a palladium and copper-catalyzed amination (Buchwald-Hartwig (B-H) or Chan-Lam (C-L)) followed by a palladium-catalyzed intramolecular aminocarbonylation with Mo(CO)6 as CO surrogate (to avoid toxic CO handling) of readily available o-phenylenediamines and either 1,2-dibromobenzene or 2-bromophenylboronic acid. The 10,11-dihydro-5H-dibenzo[b,e][1,4]diazepinone could be synthezised in good yield using a sequential catalytic procedure, using both C-L and B-H approaches. Gratifingly, the use of the C-L reaction was more impressive, and afforded the dibenzodiazepinones in good yields (up to 45%; 2 steps) and much milder conditions using copper as the catalyst. The synthetic utility of this novel strategy was showcased by demonstrating a formal synthesis for the antipsychotic drug clozapine and to an anticancer triazole-DBDAP hybrid.

Ligand Effects of BrettPhos and RuPhos on Rate-Limiting Steps in Buchwald-Hartwig Amination Reaction Due to the Modulation of Steric Hindrance and Electronic Structure

The differences in catalytic activity between two catalyst ligands of Buchwald-Hartwig amination reaction, BrettPhos versus RuPhos, were investigated using density functional theory (DFT) calculations. The reaction process consists of three consecutive steps: (1) oxidative addition, (2) deprotonation, and (3) reductive elimination. Among them, the rate-limiting step of Pd-BrettPhos catalytic system is oxidative addition but that of Pd-RuPhos catalytic system is reductive elimination due to their differences in steric hindrance and electronic structure. It was also revealed that amines with large-size substituents or halides with electron-withdrawing groups would reduce the activation energy barriers of the reactions. The insights gained from the calculations of the Buchwald-Hartwig amination reaction would be helpful for the rational designing of new catalysts and reactions.

Palladium-Catalyzed Benzodiazepines Synthesis

This review is focused on palladium-catalyzed reactions as efficient strategies aimed at the synthesis of different classes of benzodiazepines. Several reaction typologies are reported including hydroamination, amination, C–H arylation, N-arylation, and the Buchwald–Hartwig reaction, depending on the different substrates identified as halogenated starting materials (activated substrates) or unactivated unsaturated systems, which then exploit Pd(0)- or Pd(II)-catalytic species. In particular, the use of the domino reactions, as intra- or intermolecular processes, are reported as an efficient and eco-compatible tool to obtain differently functionalized benzodiazepines. Different domino reaction typologies are the carboamination, aminoarylation, aminoacethoxylation, aminohalogenation, and aminoazidation.