Borrowing hydrogen amination: Whether a catalyst is required?

Highly Efficient Base Catalyzed N‐alkylation of Amines with Alcohols and β‐Alkylation of Secondary Alcohols with Primary Alcohols

“…Furthermore, we performed a reaction with only benzyl alcohol as substrate and found that it can be oxidized into benzaldehyde which further converts into potassium benzoate via the Cannizzaro side reaction giving yields of 13 % and 38 % potassium benzoate in the presence of 25 mol% and 100 mol% of base respectively (Scheme 2, g). These results are in line with the work reported by Chusov and coworkers and Lei and coworkers regarding the oxidation of benzyl alcohol in the presence of air and base [10,31] …”

Tandem Hydrogen‐Borrowing Dehydrogenative Coupling and Hydrodefluorination

“…[35] Specifically for hydrogenborrowing N-alkylation reactions, KOtBu has been reported to be able to perform these reactions for certain substrates at high temperatures in the absence of a transition metal catalyst. [36] With the appropriate caveats as to the role of trace metals in proposed organo-mediated coupling processes, [37][38][39] uncatalyzed DC reactivity is purportedly favoured by amines with low Bordwell acidity, solvents with low dielectric constants, and high reaction temperatures. Indeed, for DC of aniline with benzyl alcohol, an unsaturated imine product (see Supporting Information, Scheme S5) can be obtained with 27% conversion ( 1 H NMR) by heating a mixture of starting materials in the presence of two equivalents of KOtBu and no added ruthenium.…”

Role of ancillary ligands in selectivity towards acceptorless dehydrogenation versus dehydrogenative coupling of alcohols and amines catalyzed by cationic ruthenium(ii)–CNC pincer complexes

“…Metal-free base catalyzed N-alkylation of amines have also been reported with alcohols. [62][63][64] However, the marked reversal in the catalytic activity (TH and AAD vs. ADC) of complexes containing the PPh 3 ligand (3a, 3b, and 3c) indicates the role played by these complexes during the imine formation. Analysis of the mass spectrogram of the catalytic mixture provided proof of a metal bound aldehyde, bound as a chelate after a Murai type C-H activation of the phenyl ring.…”

“…33,[45][46][47] Moreover, alternative synthesis of imines and N-alkylation of amines by alcohols have also been reported without transition metal catalysts. [62][63][64] The vast applications of these related reactions in synthetic chemistry and new energy pathways highlight the need for new catalysts that are selective towards one type of reaction. Although the effects of the reaction temperature or steric effects due to ligands or substituents on the substrates are common, the electronic effects of spectator ligands on selectivity control have not been documented.…”