Redox‐Triggered CC Coupling of Diols and Alkynes: Synthesis of β,γ‐Unsaturated α‐Hydroxyketones and Furans by Ruthenium‐Catalyzed Hydrohydroxyalkylation

Abstract

Direct ruthenium‐catalyzed CC coupling of alkynes and vicinal diols to form β,γ‐unsaturated ketones occurs with complete levels of regioselectivity and good to complete control over the alkene geometry. Exposure of the reaction products to substoichiometric quantities of p‐toluenesulfonic acid induces cyclodehydration to form tetrasubstituted furans. These alkyne‐diol hydrohydroxyalkylations contribute to a growing body of merged redox‐construction events that bypass the use of premetalated reagents and, hence, stoichiometric quantities of metallic by‐products.

Ruthenium-Catalyzed Transfer Hydrogenation for C–C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs

“…For example, in the presence of the ruthenium(0) catalyst derived from Ru 3 (CO) 12 and PCy 3 , vicinal diols and alkynes react to form α-hydroxy β,γ-unsaturated ketones as single geometrical isomers (Scheme 12). 70 Here, it was found that carboxylic acid cocatalysts dramatically increase rate and conversion. A catalytic mechanism that accounts for the effect of the carboxylic acid cocatalysts is as follows.…”

A Review of some catalysts and promoters used in organic transformations

“…[80] Ruthenium-catalysed C-C coupling of alkynes and vicinal diols shows high levels of region selectivity. [81] Aldol condensation followed by selective hydrogenation over ruthenium catalyst was proven to be efficient for cyclamen aldehyde synthesis. [82] The catalytic effect of ruthenium(III) in oxidation of alginate and pectate by chromic acid in perchlorate solution was followed.…”

Diols as Dienophiles: Bridged Carbocycles via Ruthenium(0)‐Catalyzed Transfer Hydrogenative Cycloadditions of Cyclohexadiene or Norbornadiene

“…Transfer hydrogenolytic cleavage of the resulting metallacycles IIIA and IIIC mediated by diol 2 a or ketol dehydro ‐ 2 a releases the cycloadducts 3 a and 4 a . The carboxylic acid cocatalyst is postulated to accelerate transfer hydrogenolysis of the sterically congested metallacycle IIIA via protonolytic cleavage of a ruthenium–oxygen bond to form a more accessible and substitutionally labile ruthenium carboxylate (not shown) . It should be noted that although ethylene and α‐olefins engage in diol‐mediated C−C coupling under the conditions of ruthenium(0) or osmium(0), catalysis, the more highly substituted mono‐olefins cyclohexene and norbornene do not engage in C−C coupling in the presence or absence of a carboxylic acid cocatalyst, likely due to unfavorable equilibria associated with the reversible nature of the oxidative coupling event .…”