Enabling the Facile Synthesis of Arenes by Transition Metal Catalyzed Decarbonylation Methodology

Transition metal-catalyzed decarbonylation is an essential paradigm of synthetic organic chemistry. Decarbonylation offers a unique pathway to decoding the skeletal structure of arenes and enabling easy synthesis of structurally complicated molecules. Due to the omnipresence of carbonyl groups in a wide array of synthetically important complex molecules, the variety and scope of these transformations are enormous. As a result, the development of transition metal catalysts in such a simple decarbonylation reaction ranks among one of the most important topics in synthetic organic chemistry. Transition metals that have been employed range from 3d metals like V to second-row transition metals like Pd. The growing potential of this methodology has driven the pioneers of synthetic organic chemistry into delving into the details of this transition metal-catalyzed decarbonylation pathways. This review aims to take the readers through the employment of transition metals in various decarbonylation processes developed by our group, sticking not only to the scope and diversification of synthetically complex molecules, but also enabling the readers to understand the mechanistic insights, through computational and kinetic studies put forward in such reaction protocol, hoping to pave the way for future organic chemists to delve and hopefully solve the unique problems associated with this protocol.

Preparation of Polyfunctional Biaryl Derivatives by Cyclolanthanation of 2-Bromobiaryls and Heterocyclic Analogues Using nBu2 LaCl⋅4 LiCl

Various aryl- and heteroaryl-substituted 2-bromobiaryls are converted to cyclometalated lanthanum intermediates by reaction with nBu2 LaCl⋅4 LiCl. These resulting lanthanum heterocycles are key intermediates for the facile preparation of functionalized 2,2'-diiodobiaryls, silafluorenes, fluoren-9-ones, phenanthrenes, and their related heterocyclic analogues. X-ray absorption fine structure (XAFS) spectroscopy was used to rationalize the proposed structures of the involved organolanthanum species.

Heterogeneous One-Pot Carbonylation and Mizoroki-Heck Reaction in a Parallel Manner Following the Cleavage of Cinnamaldehyde Derivatives

Carbon monoxide (CO) and styrene derivatives that can be both generated by a palladium on carbon (Pd/C)-catalyzed carbon-carbon (C-C) bond cleavage reaction of cinnamaldehyde derivatives were effectively utilized in further palladium-catalyzed C-C bond forming reactions in a direct and practical way. CO derived from simple and affordable CO carriers such as cinnamaldehyde or terephthalaldehyde was efficiently employed in the in situ CO fixation with various aromatic iodides through a palladium-catalyzed carbonylation followed by an inter- or intramolecular coupling reaction with alcohols to afford the corresponding esters or lactones, respectively. Styrene derivatives were also efficient substrates in an in situ Mizoroki-Heck-type cross-coupling reaction with aryl iodides, leading to the effective formation of asymmetric stilbenes. The decarbonylation of cinnamaldehyde derivatives and the subsequent independent syntheses of both esters/lactones and 1,2-diarylethenes could be achieved in a virtual one-pot and in situ reaction using a H-shaped pressure-tight glass-sealed tube consisting of two independent but laterally connected reaction tubes in the gas space.

Rh(I) -Catalyzed Intramolecular Carbonylative C-H/C-I Coupling of 2-Iodobiphenyls Using Furfural as a Carbonyl Source

Synthesis of fluoren-9-ones by a Rh-catalyzed intramolecular C-H/C-I carbonylative coupling of 2-iodobiphenyls using furfural as a carbonyl source is presented. The findings indicate that the rate-determining step is not a C-H bond cleavage but, rather, the oxidative addition of the C-I bond to a Rh(I) center.