Carbonylative Suzuki coupling reactions catalyzed by ONO pincer–type Pd(II) complexes using chloroform as a carbon monoxide surrogate

Carbonylative Transformations Using a DMAP-Based Pd-Catalyst through Ex Situ CO Generation

A phosphine-free, efficient protocol for aminocarbonylation and carbonylative Suzuki-Miyaura coupling has been developed using a novel palladium complex, [PdII(DMAP)2(OAc)2]. The complex was successfully synthesized using a stoichiometric reaction between PdII(OAc)2 and DMAP in acetone at room temperature and characterized using single-crystal X-ray analysis. Only 5 mol % catalyst loading was sufficient for effective carbonylative transformations. "Chloroform-COware" chemistry was utilized for safe and facile insertion of the carbonyl unit using chloroform as an inexpensive CO source in a two-chamber setup. Various value-added pharmaceutically relevant compounds such as CX-516, CX-546, and farampator were synthesized using the technique. Furthermore, the commercially designed COware was engineered to COware-RB setup for sequential one-pot synthesis of indenoisoquinolines (topoisomerase I inhibitors).

Synthesis and structure of Pd(II) pincer complexes: catalytic application in β-alkylation of secondary alcohols involving sequential dehydrogenation of alcohols via the borrowing hydrogen approach

Herein, we report an efficient and sustainable approach for the selective synthesis of ketones by palladium pincer catalyzed β-alkylation of secondary alcohols with aromatic primary alcohols via the borrowing hydrogen (BH) approach for the first time. A set of new Pd(II) ONO pincer complexes was synthesized and characterised by elemental analysis and spectral techniques (FT-IR, NMR and HRMS). The solid-state molecular structure of one the complexes was corroborated by X-ray crystallography. A range of α-alkylated ketone derivatives (25 examples) was obtained in excellent yields up to 95% through sequential dehydrogenative coupling of secondary and primary alcohols with 0.5 mol% catalyst loading with a substoichiometric amount of the base. Control experiment studies were carried out for the coupling reactions which revealed that the reaction involves an aldehyde, a ketone and chalcone intermediates, and eventually established the borrowing hydrogen strategy. Gratifyingly, this protocol is simple and atom economical, with water/hydrogen as byproducts. In addition, large-scale synthesis also demonstrated the synthetic usefulness of the present protocol.

Palladium-Catalyzed Aminocarbonylation of Isoquinolines Utilizing Chloroform-COware Chemistry

The carbonyl group forms an integral part of several drug molecules and materials; hence, synthesis of carbonylated compounds remains an intriguing area of research for synthetic and medicinal chemists. Handling toxic CO gas has several limitations; thus, using safe and effective techniques for in or ex situ generation of carbon monoxide from nontoxic and cheap precursors is highly desirable. Among several precursors that have been explored for the generation of CO gas, chloroform can prove to be a promising CO surrogate due to its cost-effectiveness and ready availability. However, the one-pot chloroform-based carbonylation reaction requires strong basic conditions for hydrolysis of chloroform that may affect functional group tolerability of substrates and scale-up reactions. These limitations can be overcome by a two-chamber reactor (COware) that can be utilized for ex situ CO generation through hydrolysis of chloroform in one chamber and facilitating safe carbonylation reactions in another chamber under mild conditions. The versatility of this "Chloroform-COware" technique is explored through palladium-catalyzed aminocarbonylation of medicinally relevant heterocyclic cores, viz., isoquinoline and quinoline.

Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

A variety of chromone fused cyclopentanones are efficiently generated in good to high yields via palladium-catalyzed [2 + 2 + 1] annulation, in which cyclopropenone was utilized for the first time as the sole CO surrogate in the carbonylation process.