Gold(I)-Catalyzed Cross-Coupling Reactions of Arenediazonium Salts with Alkynoic Acids
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old(I)-Catalyzed Cross-Coupling Reactions of Arenediazonium Salts with Alkynoic Acids J. N. Abramsa,* and B. K. Chia a
Department of Chemistry, Texas A&M University–Kingsville, Kingsville TX, 78363 USA *e-mail: [email protected] Received February 26, 2020; revised April 20, 2020; accepted April 21, 2020
Abstract—The reaction of simple alkynoate salts with isolated arenediazonium tetrafluoroborate salts that had been pre-conditioned with the gold(I) catalyst AuCl(Me2S) led to the formation of cross-coupled products via a decarboxylative Sonogashira reaction process in modest yield and under mild conditions. The major byproduct is a defunctionalized aryl moiety stemming from the diazonium salt, which competitively forms via hydrodediazonation. Good functional group tolerance and reaction site selectivity were attained in this limited investigation. Keywords: Sonogashira, decarboxylative, diazonium salt, alkanoic acid, gold(I)
DOI: 10.1134/S1070428020070180 INTRODUCTION Arguably, there exists no fundamental class of transformations that has been as impactful to organic research as organometallic cross-coupling protocols, which greatly enhance the chemist’s ability to synthesize complex organic molecules. Over the past several decades, various reactions have been developed that have provided the organic chemist a far greater number of options in the quest for efficient stepeconomical transformations toward targeted natural product synthesis and drug design. Historically, the pioneering work of several independent research groups in the 1970s who employed metal-mediated reactions between aryl halides and terminal phenyl acetylenes culminated in the Sonogashira reaction, which we utilize today, abetted by milder reaction conditions than predecessors’ efforts. The employment of a palladium(0) species [1] alone or in combination with a stoichiometric quantity of copper(I) co-catalyst has enabled robust C(sp2)–C(sp) coupling regimens between aryl or vinyl halides (or pseudohalides) and terminal alkynes. Despite its
evolution over time to a position of high regard and popularity as a cornerstone methodology, the Sonogashira reaction is certainly not without its drawbacks. The use of a copper(I) co-catalyst is recognized as a double-edged sword. While it enables the coupling to take place at modest temperatures, it can suffer the misfortunes of furnishing the homocoupling or socalled Glaser or Eglinton coupling [2] adducts via their in situ formed copper acetylide intermediate species, particularly if proper deoxygenation techniques are not employed. However, the operational simplicity of having an additional air-tolerant mix-and-stir reaction procedure in order to avoid the need for Schlenk line techniques would potentially further expand this C(sp)-C(sp2) coupling regimen. One such interesting rendition of the classical Sonogashira reaction involves the use of an alkanoic acid acting as a terminal alkyne surrogate that is unmasked through a metal-mediated decarboxylative process [3] to produce metal–carbon bonds, thu
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