Chemoselective One-Pot Synthesis of Functionalized Amino-azaheterocycles Enabled by COware

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).

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.

Regio- and Stereoselective Hydroiodination of Internal Alkynes with Ex Situ-Generated HI

Herein, we report an efficient and practical hydroiodination of internal alkynes using HI generated ex situ from the readily available triethylsilane and I₂. This system offers high regio- and stereoselectivity to afford (E)-vinyl iodides in good yields under mild conditions. Furthermore, the hydroiodination reaction shows high functional group tolerance toward alkyl, methoxy, halogen, trifluoromethyl, cyano, ester, halomethyl, acid-sensitive silyl ether, and acetal moieties.

One-Pot Suzuki-Hydrogenolysis Protocol for the Modular Synthesis of 2,5-Diaryltetrazoles

2,5-Diaryltetrazoles are a diverse range of compounds of considerable interest within the field of photochemistry as a valuable precursor of the nitrile imine 1,3-dipole. Current literature approaches toward this heterocycle remain unsuitable for the practical synthesis of a library of these derivatives. Herein, we disclose the development of a modular approach toward 2,5-diaryltetrazoles compatible with an array-type protocol, facilitated by a tandem Suzuki-hydrogenolysis approach.

Ex situ gas generation for lab scale organic synthesis

This review discusses recent examples of ex situ generated gaseous reagents, and their use in organic synthesis.

Synthesis of aryl-substituted quinolines and tetrahydroquinolines through Suzuki–Miyaura coupling reactions

The synthesis and characterization of substituted (trifluoromethoxy, thiomethyl, and methoxy) phenyl quinolines is described. Dichlorobis(triphenylphosphine)palladium(II)-catalyzed Suzuki–Miyaura cross-coupling of 6-bromo- and 6,8-dibromo-1,2,3,4-tetrahydroquinolines, 5-bromo-8-methoxyquinoline, and 5,7-dibromo-8-methoxyquinoline with substituted phenylboronic acids affords the corresponding 6-aryl- (13a–d), 6,8-diaryl- (14a–c), 5-aryl- (15), and 5,7-diaryl- (16b, c) tetrahydroquinolines and quinolines in high yields (68%–82%). The structures of all the products are characterized by 1H NMR, 13C NMR,19F NMR, and Fourier transform infrared spectroscopy and by elemental analysis.

Organocatalytic aza-Michael Reaction to 3-Vinyl-1,2,4-triazines as a Valuable Bifunctional Platform

An unprecedented catalytic aza-Michael addition to substituted 3-vinyl-1,2,4-triazines, as original bifunctional platforms for the domino conjugate addition inverse-electron-demand hetero-Diels-Alder/retro-Diels-Alder ( ihDA/ rDA) reaction, was achieved using the highly acidic triflimide as an organocatalyst. Based on the use of alkoxyamine nucleophiles, this sequence not only highlights a rare example of the catalytic aza-Michael reaction to alkenylazaarenes but also proves to be useful for the elaboration of an array of biorelevant tetrahydro-[1,6]-naphthyridines.

Cyclopentyl Methyl Ether: An Elective Ecofriendly Ethereal Solvent in Classical and Modern Organic Chemistry

Solvents represent one of the major contributions to the environmental impact of fine-chemical synthesis. As a result, the use of environmentally friendly solvents in widely employed reactions is a challenge of vast real interest in contemporary organic chemistry. Within this Review, a great variety of examples showing how cyclopentyl methyl ether has been established as particularly useful for this purpose are reported. Indeed, its low toxicity, high boiling point, low melting point, hydrophobicity, chemical stability towards a wide range of conditions, exceptional stability towards the abstraction of hydrogen atoms, relatively low latent heat of vaporization, and the ease with which it can be recovered and recycled enable its successful employment as a solvent in a wide range of synthetic applications, including organometallic chemistry, catalysis, biphasic reactions, oxidations, and radical reactions.