The Ligand Free Palladium(II)-Catalyzed Regioselective 1,2-Addition of Enol Silanes to Quinones to Access 4-Hydroxy-4-(2-oxo-2-arylethyl)cyclohexadien-1-ones and Synthetic Applications

Efficient amidation of weak amines: synthesis, chiral separation by SFC, and antimicrobial activity of N-(9,10-dioxo-9,10-dihydroanthracen-1-yl) carboxamide

An effective and straightforward method for the synthesis of 1-aminoanthracene-9,10-dione carboxamides by coupling a weakly reactive amine, 1-aminoanthracene-9,10-dione, and sterically hindered carboxylic acids was achieved using COMU as the coupling agent. Furthermore, making use of the advantages associated with the super-critical fluid chromatography (SFC) technique, a simplified and straightforward method for the chiral separation of optically active amide derivatives from the impurities associated with the reaction mixture, in a single step, was demonstrated. The antimicrobial activity of selected 1-aminoanthracene-9,10-dione carboxamides was studied. Advanced NMR and other spectral techniques were used for the thorough characterization of all the compounds. This study provides a general and simplified method for coupling a weak amine with a sterically hindered acid using COMU as a coupling agent, and demonstrates the separation of optically pure compounds from reaction related impurities in a single step using SFC, and identification of amide derivatives of 1-aminoanthracene-9,10-dione as potential antimicrobial agents.

Examining the Scope of Deriving β-Aryl Enones from Enol Silanes as Ketone Equivalents via Pd(II)-Mediated Sequential Dehydrosilylation and Arylation

Silyl enol ethers were examined as a masked source of saturated ketones to derive β-aryl enones and their derivatives by dehydrosilylation to generate enones in situ and subsequent oxidative arylation with arylboronic acids as transmetallation coupling partners using relayed Pd(II) catalysis in one pot under base-free conditions. Oxygen was found to be an efficient and green oxidant to enable both dehydrosilylation of enol silanes and arylation. Additionally, arylation conditions can be custom-designed to take advantage of aryl halides as an alternative source of arylating agents. The preparative scope was investigated with 35 examples (up to 95% yield), and mechanistic studies implied a cationic Pd(II)-based catalytic system.

Synthetic Access to α-Oxoketene Aminals by the Nucleophilic Addition of Enol Silane-Derived Palladium(II) Enolates to Carbodiimides

Synthetically important α-oxoketene aminal intermediates can now be accessed from readily available and inexpensive carbodiimides as starting materials via the nucleophilic addition of palladium enolates derived from enol silane precursors. This operationally simple method features mild reaction conditions, including open air atmosphere, ligand-free metal catalysis, broad substrate scope, and multi-gram scalability. Select synthetic applications that take advantage of the enamine character of α-oxoketene aminals and involve C-nucleophilic additions to electrophilic systems, including an α,β-unsaturated ester, an azo dicarboxylate, an aralkyl halide, and an aldehyde, are demonstrated.