Ruthenium‐Catalyzed Hydrocarboxylation of Internal Alkynes

Abstract

The application of the highly efficient ruthenium catalyst [Ru(CO)2{P(p‐CF3–C6H4)3}2(O2CPh)2] (1) in the selective syn‐addition of carboxylic acids to internal alkynes, yielding valuable trisubstituted enol esters with (E)‐configuration, is described. All reactions feature excellent stereoselectivities and good regioselectivities. The regioselectivity is dictated by electronic and steric aspects of the alkyne substituents and the acidity of the carboxylic acid. The catalytic activity can be significantly increased by the addition of catalytic amounts of B(C6F5)3. Relative to known catalysts for the synthesis of (E)‐enol esters, this methodology offers improved selectivity and requires lower catalyst loadings. Moreover, a broad range of alkynes and carboxylic acids can be successfully converted to their corresponding (E)‐enol esters in high yields.

Porous Magnesium Oxide by Twin Polymerization: From Hybrid Materials to Catalysis

“…Calcinated MgO_1 and MgO_2 obtained through twin polymerization (Scheme 2) were used as catalysts in the Meerwein-Ponndorf-Verley (= MPV) reduction of carbonyl compounds like cyclohexanone, [15,84] benzaldehyde [11,13,85,86] and crotonaldehyde. [12,14] Hence, the latter compounds were treated with catalytic amounts of MgO_1 and MgO_2 in iso-propanol and in the presence of a defined amount of acenaphtene as an internal standard [87] in a sealed Schlenk tube at 85 °C. Samples were taken after centrifugation and subsequent filtration through a syringe filter and measured via GC-MS (Table 3).…”

Recent Advances in the Synthesis of Carboxylic Acid Esters

“…Two examples for the regio-and E-selective addition of carboxylic acids onto "internal" alkynes have been reported (Scheme 19 catalyst afforded the corresponding E-enol esters in up to 99% yield with the extremely high E-selectivity [139]. This catalytic system also achieved the regio-and stereoselective addition of carboxylic acids to unsymmetrical internal alkynes, in which the E/Z ratio reached up to 72:28.…”

The intermolecular hydro-oxycarbonylation of internal alkynes: current state of the art

“…72,73 In this regard, in combination with the Lewis acid B(C6F5)3, complex 5 was able to catalyze the addition of different carboxylic acids to both activated and unactivated internal alkynes with complete syn-selectivity, affording a broad range of trisubstituted (E)-enol esters in high yields (Scheme 5). 73 Unfortunately, in the case of unsymmetrically substituted substrates, the regioselectivity of the process could not be controlled, and mixtures of the two regioisomeric syn-addition products 6 and 7 were in all the cases obtained. However, we must note that some influence of the C≡C bond substituents on the regioselectivity of the process was observed, increasing as the substituents become more electronically or sterically dissimilar.…”