Mechanistic insights into hydroacylation with non-chelating aldehydes

Abstract

Rhodium catalysts with small-bite-angle diphosphines enable branched-selective hydroacylation of 2-vinylphenols via C–H activation of non-chelating aldehydes.

Well‐Defined and Robust Rhodium Catalysts for the Hydroacylation of Terminal and Internal Alkenes

“…13b H/D exchange was observed into free 4 a during catalysis, suggesting reversible aldehyde and alkene binding. The measured KIE is similar to other systems in which reductive elimination is proposed to be turnover‐limiting,8b, 13 rather than irreversible CH activation (KIE ≈2.57c, 18), and is likely an equilibrium isotope effect 21. Addition of just 1‐octene to 3 a results in isomerization to give a mixture of internal alkenes, that are not seen during catalysis when 4 a is also present.…”

“…[4] Control of decarbonylation can come from substrate chelation, such as b-substituted aldehydes or alkenes, [1a, 5] whereas the use of the hemilabile ligand bis-[2-(diphenylphosphino)phenyl]ether (DPEphos) that reversibly binds to the vacant site through aRh···O linkage (Scheme 2), affords al ong-lived catalyst, but activity is not significantly enhanced resulting in ar ather limited scope of substrates. [6] An alternative approach is to increase the rate of reductive elimination of ketone product, as tep that is often (although not exclusively [7] )t he turnover-limiting process in hydroacylation. [3a,8] Wide-bite-angle,o rs terically bulky,l igands have this effect, but also change the ratio of alkene versus aldehyde hydroacylation [9] or the linear/branched selectivity.…”

Intermolecular Markovnikov-Selective Hydroacylation of Olefins Catalyzed by a Cationic Ruthenium–Hydride Complex

“…Dong and co-workers recently reported a similar Hammett ρ value in the catalytic hydroacylation of 4-nitro-2-vinylphenol with para -substituted benzaldehydes. 7g …”

Green Metal‐Free Photochemical Hydroacylation of Unactivated Olefins

“…In 2000, Jun introduced the use of 2‐amino‐3‐picoline as an additive to Rh‐catalyzed hydroacylation at elevated temperature, since imine formation with the carbonyl group facilitates metal complexation (Scheme C) . Dong has extensively researched the area, with the limitation being the use of only ortho ‐hydroxy aromatic substrates, in order to provide the reactive Rh complex (Scheme D) . Along the same lines, Willis has employed β‐carbonyl moieties to facilitate coordination (Scheme E) .…”