Hydrostannation of Alkynes

International audienceIn this review, we present an overview of hydrostannation of alkynes until the end of 2018. Mechanism of the tin hydride addition on a triple bond is discussed at the beginning of this review in the presence of metal catalysts as Pd, Ru-based complexes, Lewis acids and under radical conditions. Then, stereoselectivity as well as regioselectivity aspects of tin hydride addition on the carbon triple bond is discussed using metal-catalysis, radical conditions or Lewis acids. In each of these items, the reactions will be studied for terminal alkynes and then, for internal alkynes. Applications of hydrostannation of alkynes using metal-catalysis is presented in a variety of total syntheses with Pd, Mo, Rh and Ru-complexes to provide highly functionalized vinyl stannanes derivatives as key-intermediates. Comparison with other methods providing vinyl stannanes using metallostannation followed by protonation is presented before the last section dealing with a summary of classical experimental conditions used to achieve the hydrostannation of alkynes

Synthesis of Substituted Benzils from Diarylalkyne Oxidation

International audienceIn this review, oxidation of diarylalkynes leading to functionalized benzils (di(het)aryl-1,2-diketones) is summarized. Some synthetic "one pot" transformations of internal arylalkynes leading to the construction of heterocycles are presented

Chlorotrimethylsilane and Sodium Iodide: A Remarkable Metal-Free Association for the Desulfurization of Benzylic Dithioketals under Mild Conditions

International audienceA novel metal-free process allowing the reductive desulfurization of various benzylic dithioketals to afford diarylmethane and benzylester derivatives with good to excellent yields is reported. At room temperature, this mild reduction process requires only the use of TMSCl and NaI in CH2Cl2 and tolerates a large variety of functional groups

Desulfurization of Thioketals into Methylene and Methyl Derivatives: Nickel or not Nickel?

International audienceIn this review, the desulfurization of thioacetals and thioketals leading to methyl and methylene derivatives is summarized through metal and metal-free methodologies. In the section concerning the use of metals for desulfurization reactions, we will be successively presenting and discussing all methods requiring Ni and Ni derivatives as reducing agents and other examples in which metals were used to generate solvating electrons as reducing species. The following section will concern the use of other desulfurizing agents as metal-hydrides (Bu3SnH, Et3SiH) and metal-free desulfurization reactions of thioketals. The functional group tolerance of the presented methods with functionalized and sensitive substrates will be discussed

One-pot hydrosilylation–protodesilylation of functionalized diarylalkynes: a highly selective access to Z-stilbenes. Application to the synthesis of combretastatin A-4

International audienceAn efficient stereoselective synthesis of Z-stilbenes has been developed from diarylalkynes via a new hydrosilylation-protodesilylation process. Scope and limitation of this method to prepare stereoselectively a wide range of (Z)-stilbenes in a one-pot way is presented. A concise application to the preparation of combretastatin A-4 (CA-4), a vascular targeting agent inhibitor of tubulin polymerisation is described

Expeditious synthesis of 1,1-diarylethylenes related to isocombretastatin A-4 (isoCA-4) via palladium-catalyzed arylation of N-tosylhydrazones with aryl triflates

International audienceA quick and efficient entry to 1,1-diarylethylenes via the reaction of poly-oxygenated aryl N-tosylhydrazones with aryl triflates is described. The reaction employs the catalytic system Pd(OAc)2/XPhos, tBuOLi as the base and dioxane as the solvent. A variety of substituents on both coupling partner's hydrazones and triflates are tolerated. This procedure provides a complementary route to the existing methods for the access to 1,1-diarylethylenes of biological interest

Tributyltin Hydride in NMP-Promoted Reduction of Acid Chlorides to Aldehydes under Transition-Metal-Free Conditions

International audienceTributyltin hydride in NMP was used for the partial reduction of various functionalized acid chlorides at room temperature. This metal-free procedure allowed the synthesis of a range of (hetero)aromatic-and aliphatic aldehydes in good to excellent yields

One-Pot Synthesis of 2-Styrylindoles from Ortho -Substituted Chloroenynes

International audienceA facile one pot synthesis of 2-styrylindoles, through Suzuki-arylation of ortho-substituted chloroenynes followed by N-cyclization and N-demethylation has been developed. A variety of 2-styrylindoles were obtained in good to excellent yields and were evaluated for their anticancer properties

MPHT-Promoted Bromocyclization of ortho-Substituted Arylalkynes: Application to the Synthesis of 2-Substituted 3-Bromobenzofurans and -Benzo[b]thiophenes

International audienceA convenient and general approach to the synthesis of 2‐substituted 3‐bromobenzofurans and ‐benzothiophenes was developed. The procedure is based on the cyclization of ortho‐substituted arylalkynes in the presence of N‐methylpyrrolidin‐2‐one hydrotribromide (MPHT) as a soft and easy‐to‐handle electrophilic brominating reagent. Under mild reaction conditions, MPHT promoted the bromocyclization of various enynes and diynes as well as arylalkynes to give 2‐substituted 3‐bromobenzofurans and ‐benzothiophenes in high to excellent yields. Subsequent functionalization by palladium‐catalyzed coupling reactions at the C–Br bond afforded general access to 2,3‐disubstituted benzofurans and benzothiophenes of biological interest

Gold versus Palladium: A Regioselective Cycloisomerization of Aromatic Enynes

International audienceAromatic enynes can be transformed into arylnaphthalenes or benzofulvenes depending on the reaction conditions. Under gold(I) catalysis, exclusive or major 6-endo-dig cyclization took place leading to arylnaphthalenes. However, a catalytic system based on palladium iodide/1,3-Bis(diphenylphosphino)propane, in the presence of cesium carbonate as a base was necessary to furnish exclusively 5-exo-dig cyclization pattern, regardless to the electronic effects of the substituents. In the latter transformation, a mechanistic study (Kinetic Isotopic Effect, Density Functional Theory) involving a C-H activation is suggested for the exclusive benzofulvenes formation