RESUMEN

Shuttle hetero-difunctionalization reaction, in which two chemically distinct functional groups are transferred between two molecules, has long been an unmet goal due to the daunting challenges in controlling the chemo-, regio-, and stereoselectivity. Herein, we disclose an electrochemistry enabled shuttle reaction (e-shuttle) to selectively transfer one RS- and one X- group between ß-halosulfides and unsaturated hydrocarbons via a consecutive paired electrolysis mechanism. The preferential anodic oxidation of one anion over the other, which is controlled by their distinct redox potentials, plays a pivotal role in controlling the high chemoselectivity of the process. This easily scalable methodology enables the construction of a myriad of densely functionalized ß-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g., 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS-Br reagents. In a broader context, these results open up new strategies for selective shuttle difunctionalization reactions.

RESUMEN

A rhodium-catalyzed anti-Markovnikov hydroiodination of aromatic and aliphatic terminal alkynes is reported. Depending on the choice of ligand and substrate, either (E)- or (Z)-configured alkenyl iodides are obtained in high to exclusive isomeric purity. The reaction exhibits a broad substrate scope and high functional group tolerance, employing easily accessible or commercially available aliphatic iodides as HI surrogates through a shuttle process. The synthesized vinyl iodides were applied in several C-C and C-heteroatom bond-forming reactions with full retention of the stereoselectivity. The developed method could be used to significantly shorten the total synthesis of a marine cis-fatty acid. Additionally, initial deuterium-labeling experiments and stoichiometric reactions shed some light on the potential reaction mechanism.

Asunto(s)

Rodio , Alquinos , Yoduros , Catálisis , Isomerismo

RESUMEN

We report an efficient and broadly applicable palladium-catalyzed iodination of inexpensive and abundant aryl and vinyl carboxylic acids via in situ activation to the acid chloride and formation of a phosphonium salt. The use of 1-iodobutane as iodide source in combination with a base and a deoxychlorinating reagent gives access to a wide range of aryl and vinyl iodides under Pd/Xantphos catalysis, including complex drug-like scaffolds. Stoichiometric experiments and kinetic analysis suggest a unique mechanism involving C-P reductive elimination to form the Xantphos phosphonium chloride, which subsequently initiates an unusual halogen exchange by outer sphere nucleophilic substitution.

RESUMEN

An efficient palladium-catalyzed chlorocarbonylation of aryl (pseudo)halides that gives access to a wide range of carboxylic acid derivatives has been developed. The use of butyryl chloride as a combined CO and Cl source eludes the need for toxic, gaseous carbon monoxide, thus facilitating the synthesis of high-value products from readily available aryl (pseudo)halides. The combination of palladium(0), Xantphos, and an amine base is essential to promote this broadly applicable catalytic reaction. Overall, this reaction provides access to a great variety of carbonyl-containing products through in situ transformation of the generated aroyl chloride. Combined experimental and computational studies support a reaction mechanism involving in situ generation of CO.

RESUMEN

Described herein are two different methods for the synthesis of vinyl halides by a shuttle catalysis based iridium-catalyzed transfer hydrohalogenation of unactivated alkynes. The use of 4-chlorobutan-2-one or tert-butyl halide as donors of hydrogen halides allows this transformation in the absence of corrosive reagents, such as hydrogen halides or acid chlorides, thus largely improving the functional-group tolerance and safety profile of these reactions compared to the state-of-the-art. This method has granted access to alkenyl halide compounds containing acid-sensitive groups, such as tertiary alcohols, silyl ethers, and acetals. The synthetic value of those methodologies has been demonstrated by gram-scale synthesis where low catalyst loading was achieved.

RESUMEN

The first example of an efficient and direct dehydrogenative boration of alkenes for vinyl boronate ester synthesis was achieved using a zirconium catalyst. Our methodology avoids using precious transition metals, additional hydrogen acceptors, high temperatures, and long reaction times, which were required to overcome the reducing ability of borane, to give alkyl boronate esters. Detailed mechanistic studies revealed a reversible reaction pathway and further suggested applying the zirconium complex as a "shuttle catalyst" for transfer boration, which thus sidesteps the use of relatively sensitive borane.

RESUMEN

Shuttle catalysis has recently emerged as a powerful new concept that provides a platform for performing both functionalization and defunctionalization reactions. In this concept article, applications of shuttle catalysis as a novel strategy in organic synthesis are discussed. This includes using forward shuttle catalysis reactions for challenging bond-forming processes that avoid the use of hazardous chemicals. Shuttle catalysis also facilitates the transfer of reactive functionality as a route to procure a broad range of compounds using one simple procedure. Reverse shuttle catalysis reactions are also discussed as a method for the valorization of biomass and waste materials. Another area of interest, shuttle-catalysis-assisted reactions, wherein the transfer of a small molecule is utilized in a catalytic cycle, is also described. Possible future directions in this exciting new field are also suggested.