Metal-Catalyzed Intra- and Intermolecular Addition of Carboxylic Acids to Alkynes in Aqueous Media: A Review

Abstract

Abstract:The metal-catalyzed addition of carboxylic acids to alkynes is a very effective tool for the synthesis of carboxylate-functionalized olefinic compounds in an atom-economical manner. Thus, a large variety of synthetically useful lactones and enol-esters can be accessed through the intra-or intermolecular versions of this process. In order to reduce the environmental impact of these reactions, considerable efforts have been devoted in recent years to the development of catalytic systems able to operate in aqueous media, which represent a real challenge taking into account the tendency of alkynes to undergo hydration in the presence of transition metals. Despite this, different Pd, Pt, Au, Cu and Ru catalysts capable of promoting the intra-and intermolecular addition of carboxylic acids to alkynes in a selective manner in aqueous environments have appeared in the literature. In this review article, an overview of this chemistry is provided. The synthesis of β-oxo esters by catalytic addition of carboxylic acids to terminal propargylic alcohols in water is also discussed.

Iron(III)‐Catalyzed Hydration of Unactivated Internal Alkynes in Weak Acidic Medium, under Lewis Acid‐Assisted Brønsted Acid Catalysis

“…Protonation of the alkyne by hydronium ions or by Fe III ‐activated AcOH yields intermediate alcohol or vinylic ester, which undergo rapid tautomeric rearrangement or hydrolysis to afford the final hydration product.…”

Permethylated NHC‐Capped α‐ and β‐Cyclodextrins (ICyDMe) Regioselective and Enantioselective Gold‐Catalysis in Pure Water

“…Another classical gold-catalyzed reaction is the intramolecular addition of carboxylic acids to alkynes, [49] which has been developedi na queous media, [50] and with water-soluble NHC ligands. [26,28,30,51] Therefore, the catalytic activity of both 5a and 5b was tested in the lactonization of three g-alkynoic acids (15)(16)(17), in pure water (Scheme 3).…”

Metal-Catalyzed Synthesis and Transformations of β-Haloenol Esters

“…For example, alkenyl halides are widely used as substrates in transition metal-catalyzed cross-coupling reactions [1,2] and can be easily converted, through a metal-halogen exchange, into nucleophiles for 1,2additions to carbonyl compounds [3]. Enol esters are also relevant olefinic derivatives with multitude of applications in modern organic chemistry [4][5][6]. The introduction of a halogen atom on the C=C bond of the latter leads to functionalized molecules, i.e., α-and β-haloenol esters (Figure 1), in which the reactivities of the haloalkene and enol ester functionalities can be combined and potentially exploited in numerous synthetic ways.…”