Alkynes as Allylmetal Equivalents in Redox-Triggered C–C Couplings to Primary Alcohols: (Z)-Homoallylic Alcohols via Ruthenium-Catalyzed Propargyl C–H Oxidative Addition

Abstract

The cationic ruthenium catalyst generated upon the acid-base reaction of H2Ru(CO)(PPh3)3 and 2,4,6-(2-Pr)3PhSO3H promotes the redox-triggered C-C coupling of 2-alkynes and primary alcohols to form (Z)-homoallylic alcohols with good to complete control of olefin geometry. Deuterium labeling studies, which reveal roughly equal isotopic compositions at the allylic and distal vinylic positions, along with other data, corroborate a catalytic mechanism involving ruthenium(0)-mediated allene-aldehyde oxidative coupling to form a transient oxaruthenacycle; an event that ultimately defines (Z)-olefin stereochemistry.

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

“…48 Isomerization is promoted through the use of cationic ruthenium catalysts generated through the acid-base reaction of H 2 Ru(CO)(PPh 3 ) 3 and 2,4,6-(2-Pr) 3 PhSO 3 H. As corroborated by deuterium labelling studies, the cationic ruthenium complex appears to exist in equilibrium with zero-valent species that promote isomerization via propargyl C-H oxidative addition. Allene-aldehyde oxidative coupling mediated by ruthenium(0) then forms an oxaruthenacycle, which upon transfer hydrogenolysis delivers the ( Z )-homoallylic alcohols with good to complete levels of stereocontrol.…”

Alkyne Hydroacylation: Switching Regioselectivity by Tandem Ruthenium Catalysis

“…Krische proposed that Ru(0) isomerized alkynes to allenes, albeit by a C–H propargyl activation mechanism. 18 While Willis has reported allene hydroacylations with chelating aldehydes, 19 we envisioned the resulting allene would undergo metal-hydride addition to generate a metal-allyl species that could couple to non-chelating aldehydes (Figure 1b). This mechanistic step has been shown in the coupling of allenes and aldehydes to generate homoallylic alcohols.…”

Enantioselective Ruthenium-Catalyzed Carbonyl Allylation via Alkyne–Alcohol C–C Bond-Forming Transfer Hydrogenation: Allene Hydrometalation vs Oxidative Coupling

“…3). 15 In this communication, we disclose key alterations to the reaction conditions that suppress allene-carbonyl oxidative coupling of the transient allene to favor allene hydrometallation, 16 resulting in the first examples of catalytic enantioselective carbonyl allylation using alkynes as chiral allylmetal equivalents (Scheme 1, eq. 4).…”