Metal-Catalyzed Synthesis and Transformations of β-Haloenol Esters

Abstract

In the last years there has been an increasing interest in the search for protocols to obtain β-haloenol esters in an efficient and selective manner as they are versatile building blocks in synthetic organic chemistry. In this article, metal-catalyzed transformations allowing the access to both acyclic and cyclic (i.e., haloenol lactones) β-haloenol esters are reviewed. Metal-catalyzed reactions in which these molecules participate as substrates are also discussed.

Synthesis of Carbene‐Metal‐Amido (CMA) Complexes and Their Use as Precatalysts for the Activator‐Free, Gold‐Catalyzed Addition of Carboxylic Acids to Alkynes

“…[30] Gold(I) complexes has been shown to activate alkenes, allenes, alkynes, arenes, and nitriles in such transformations as hydration, hydroamination, hydrogenation, hydrophenoxylation and hydroacyloxylation (called hydrocarboxylation) reactions. [31][32][33] The hydrocarboxylation reaction involves a carboxylic acid addition to an alkyne to produce an enol-ester. By using widely available and inexpensive carboxylic acids in combination with alkynes, these substrates can be upgraded to valuable enol-esters.…”

“…Gold(I) cations are soft, carbophilic π‐acids and have increased Lewis acidity compared to other coinage metals [30] . Gold(I) complexes has been shown to activate alkenes, allenes, alkynes, arenes, and nitriles in such transformations as hydration, hydroamination, hydrogenation, hydrophenoxylation and hydroacyloxylation (called hydrocarboxylation) reactions [31–33] . The hydrocarboxylation reaction involves a carboxylic acid addition to an alkyne to produce an enol‐ester.…”

Catalytic Addition of Indole-2-Carboxylic Acid to 1-Hexyne

“…The catalytic addition of carboxylic acids to alkynes is the most straightforward and atom-economical method currently available to obtain enol esters, which are very useful intermediates for organic synthesis [1][2][3][4][5][6][7]. A large number of Groups 8-11 metal complexes able to promote the process have been reported in the literature, predominating those based on ruthenium and gold due to their exquisite regio-and stereo-selectivity [1][2][3][4][5][6][7][8].…”

“…The catalytic addition of carboxylic acids to alkynes is the most straightforward and atom-economical method currently available to obtain enol esters, which are very useful intermediates for organic synthesis [1][2][3][4][5][6][7]. A large number of Groups 8-11 metal complexes able to promote the process have been reported in the literature, predominating those based on ruthenium and gold due to their exquisite regio-and stereo-selectivity [1][2][3][4][5][6][7][8]. In this context, some years ago we disclosed that the bis(allyl)-ruthenium(IV) derivative [RuCl 2 (η 3 :η 3 -C 10 H 16 )(PPh 3 )] (C 10 H 16 = 2,7-dimethylocta-2,6-diene-1,8-diyl; 1) is an excellent catalyst for the selective Markovnikov addition of carboxylic acids to terminal alkynes [9].…”

Recent Advances in Organometallic Chemistry and Catalysis

“…The utility of these transformations was nicely illustrated by their involvement in the total synthesis of a number of naturally occurring products, as well as by the assembly of elaborated polycyclic compounds through cascade processes involving the initial cycloisomerization of an alkynoic acid. A second review article by the same author, dealing with the synthesis and catalytic transformations of β-haloenol esters, has also been included in this Special Issue [17]. In this particular class of compounds, the reactivities of the haloalkene and enol ester functionalities can be combined, making them versatile building blocks in synthetic organic chemistry.…”