Transition Metal-Catalyzed Reactions of Alkynyl Halides

Abstract

Background: Transition metal-catalyzed reactions of alkynyl halides are a versatile means of synthesizing a wide array of products. Their use is of particular interest in cycloaddition reactions and in constructing new carbon-carbon and carbon-heteroatom bonds. Transition metal-catalyzed reactions of alkynyl halides have successfully been used in [4+2], [2+2], [2+2+2] and [3+2] cycloaddition reactions. Many carbon-carbon coupling reactions take advantage of metal-catalyzed reactions of alkynyl halides, including Cadiot-Chodkiewicz, Suzuki-Miyaura, Stille, Kumada-Corriu and Inverse Sonogashira reactions. All the methods of constructing carbon-nitrogen, carbon-oxygen, carbon-phosphorus, carbon-sulfur, carbon-silicon, carbon-selenium and carbon-tellurium bonds employed alkynyl halides. Objective: The purpose of this review is to highlight and summarize research conducted in transition metalcatalyzed reactions of alkynyl halides in recent years. The focus will be placed on cycloaddition and coupling reactions, and their scope and applicability to the synthesis of biologically important and industrially relevant compounds will be discussed. Conclusion: It can be seen from the review that the work done on this topic has employed the use of many different transition metal catalysts to perform various cycloadditions, cyclizations, and couplings using alkynyl halides. The reactions involving alkynyl halides were efficient in generating both carbon-carbon and carbonheteroatom bonds. Proposed mechanisms were included to support the understanding of such reactions. Many of these reactions face retention of the halide moiety, allowing additional functionalization of the products, with some new products being inaccessible using their standard alkyne counterparts.

Metal-Catalyzed Synthesis and Transformations of β-Haloenol Esters

“…The process, which proceeds under mild conditions and tolerates the presence of several functional groups in the substrates, involves the intermolecular addition of carboxylic acids to iodoalkynes, the latter being activated towards the carboxylate anion attack by π-coordination to the in situ generated gold(I) cation [Au(PPh3)] + . As expected, the carboxylate anion adds selectively to the more electrophilic C-2 carbon of the iodoalkyne [45][46][47] and, as usually observed in the chemistry of π-alkyne-gold complexes [62], the addition takes places in an anti fashion, thus affording the olefinic products 19 in a complete regio-and stereoselective manner. With a couple of representative examples, i.e., the addition of acetic acid to 1-(chloroethynyl)-4-methylbenzene and 1-bromooct-1-yne, the authors also demonstrated the applicability of this procedure for the synthesis of related (Z)-β-chloroenol and Making use of a catalytic system composed of the gold(I) complex [AuCl(PPh 3 )] and the chloride abstractor AgPF 6 , a broad scope procedure for the preparation of acyclic (Z)-β-iodoenol esters was also recently developed by Cadierno and co-workers (Scheme 12) [59][60][61].…”

Metal‐Catalyzed Hydrofunctionalization Reactions of Haloalkynes

“…However, their synthetic utility have been for long time mainly restricted to the construction of new carbon–carbon and carbon–heteroatom bonds by coupling of the reactive carbon–halogen motif with appropriate reagents (alkynylation processes) . In recent years, the application of metal catalysts has drastically changed this scenario, and several catalytic transformations involving the π‐system of these molecules have been developed through the intermediacy of metallic species of type I , II or III (Figure ) …”

AuI-Catalyzed Hydroalkynylation of Haloalkynes

“…Traditionally, these reagents have been used as a source of acetylides via metal–halogen exchange. However, with the development of transition metal catalysis, the number of transformations in which haloalkynes are used as reaction partners has increased exponentially . Among them, amino-, , oxy-, and carboalkynylation of olefins are useful transformations for the synthesis of a variety of functionalized alkynes, while the direct C–H alkynylation and inverse Sonogashira coupling are valuable alternatives for selective introduction of alkynyl groups …”