Novel Alkynylation Methods through the Combination of Hypervalent Iodine Reagents and Alkynyl-trifluoroborate Salts

The alkyne motif is a versatile functional group often encountered in organic chemistry. It can be involved in various transformations such as the alkyne-azide cycloaddition and has found widespread application in medicinal chemistry, chemical biology and material science. The introduction of alkynes to organic molecules is often carried out from terminal alkynes by taking advantage of their acidic C-H bonds. Under basic conditions they can form lithium or transition-metal acetylides that can react with electrophiles. In recent years, the use of alkynyl-trifluoroborate salts as bench-stable nucleophilic alkynes has become an alternative approach.In addition, the last decades saw the development of reagents bearing electrophilic alkynes, allowing the introduction of triple bonds at previously inaccessible positions due to the original polarity mismatch. Ethynylbenziodoxolones (EBX), a class of hypervalent iodine reagents bearing an alkyne, have been particularly successful for this application and are nowadays routinely used.The first objective of this thesis was to develop a novel method for the synthesis of EBX reagents to facilitate their application. By using tosyloxybenziodoxolone in combination with alkynyl-trifluoroborate salts, EBXs could be formed in high yields and purity without purification. Those conditions allowed to by-pass the isolation of the reagents and to involve them directly into one-pot two-step transformations. Both polar and radical reactions were applied to this process, affording a variety of alkynylated products. Moreover, the purification-free synthesis of EBXs was used for the copper-catalyzed alkynylation of azadipeptides.The second goal of the thesis, resulting from the one-pot two-step process, was to develop the elusive acyl-EBXs. Starting from ynone-trifluoroborate salts, acyl-EBXs could be formed in solution and reacted with thiols to afford ketene dithioacetals. Both alkyl- and aryl-thiols were compatible, the latter giving access to ketene dithioarylacetals, a class of reagent scarcely explored due to a lack of synthetic access. The products could be further transformed into a variety of S-substituted heterocycles.Finally, we investigated the reactivity of alkynyl-BF3Ks to perform nucleophilic alkynylations. Taking advantage of their stability under radical conditions we developed an azido-alkynylation of alkenes using a radical-polar crossover strategy. Under photoredox catalysis and using azidobenziodazolone (ABZ) as an azide radical source, a large variety of styrenes and vinyl-substituted heterocycles could be azido-alkynylated to afford homopropargylic azides. This method tolerates different alkynyl-BF3Ks bearing alkyl- and aryl-substituents. The homopropargylic azides obtained were further transformed into bioactive homopropargylicamines or pyrroles. The reaction is proposed to occur via an overall redox-neutral radical-polar crossover mechanism.In the end, we developed 2 main types of transformation using alkynyl-BF3K. First, their reaction in a one-pot two-step alkynylation process, which simplified the application of EBXs and allowed the generation of new reagents. Second, their use as stable nucleophilic alkynes in a novel radical azido-alkynylation reaction.