NNN Pincer Ru(II)-Complex-Catalyzed α-Alkylation of Ketones with Alcohols

Abstract

A series of novel ruthenium(II) complexes supported by a symmetrical NNN ligand were prepared and fully characterized. These complexes exhibited good performance in transfer hydrogenation to form new C-C bonds using alcohols as the alkylating agents, generating water as the only byproduct. A broad range of substrates, including (hetero)aryl- or alkyl-ketones and alcohols, were well tolerated under the optimized conditions. Notably, α-substituted methylene ketones were also investigated, which afforded α-branched steric hindrance products. A potential application of α-alkylation of methylene acetone to synthesize donepezil was demonstrated, which provided the desired product in 83% yield. Finally, this catalytic system could be applied to a one-pot double alkylation procedure with sequential addition of two different alcohols. The current protocol is featured with several characteristics, including a broad substrate scope, low catalyst (0.50 mol %) loadings, and environmental benignity.

Efficient Organoruthenium Catalysts for α‐Alkylation of Ketones and Amide with Alcohols: Synthesis of Quinolines via Hydrogen Borrowing Strategy and their Mechanistic Studies

“…To our delight, for the α‐alkylation acetophenone with benzyl alcohol, this catalytic system revealed surprisingly high TON of 47000 with TOF 11750 h −1 after 4 h by using 0.001 mol % for catalyst Ru2 (Table S1 entry 10). The optimum loading of catalysts Ru1 – Ru2 for catalytic activity (0.01 mol %) of α‐alkylation ketone is lower than the values reported by Song and co‐workers (catalyst loading 0.15 mol %) . On the other hand Sahoo et al .…”

Iridium‐Catalyzed α‐Alkylation of Arylacetonitriles Using Secondary and Primary Alcohols

“…Screening of reaction temperature and time showed that 120°C and 24 h were optimal (Table 1, entries 12-15). Next, we screened solvents including xylene, NMP, DMF, dioxane, nBu 2 O and the mixed solvents of toluene and NMP in different ratios and the results showed that a 1 : 1 mixture of toluene and NMP was optimal for this transformation (Table 1, entries [16][17][18][19][20][21][22][23]. The existence of NMP might increase solubility of NaOtBu and formed secondary alcoholates in the mixed solvent.…”

Synthesis and Structures of Arene Ruthenium (II)–NHC Complexes: Efficient Catalytic α‐alkylation of ketones via Hydrogen Auto Transfer Reaction

“…In the first step, in the presence of base, the alcohol was coordinated with Ru (II)‐NHC catalyst I to form a Ru‐NHC‐alkoxide species II or II’ . Next, the β‐hydride elimination occurs in II or II’ to remove benzaldehyde A or 2‐aminobenzaldehyde A' with the formation of Ru‐hydride species III . Meanwhile, the aldehyde A or A' reacts with ketone in the presence of base to form α, β‐unsaturated ketone intermediate B or B′ .…”