Sustainable and Selective Alkylation of Deactivated Secondary Alcohols to Ketones by Non‐bifunctional Pincer N‐heterocyclic Carbene Manganese

Lan, Xiao-Bing; Ye, Zongren; Huang, Ming; Shao, Youxiang; Cai, Xiang; Liu, Yan; Ke, Zhuofeng

doi:10.1002/cssc.202000576

Cited by 54 publications

(55 citation statements)

References 101 publications

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“…(7–8)]. Similar to previous work, [26c] no incorporation of deuterium atom at the β‐position was observed, indicating the absence of H/D exchange during the reaction. The kinetic isotope effect was investigated by the coupling of 1 a with 2 a‐D or 1 a‐D with 2 a , and the k H / k D values were found to be 2.23 and 1.88, respectively, suggesting that the dehydrogenation of alcohols is most likely the rate‐determining step (RDS).…”

Section: Methodssupporting

confidence: 87%

Selective C‐alkylation Between Alcohols Catalyzed by N‐Heterocyclic Carbene Molybdenum

Liu

et al. 2021

Chemistry An Asian Journal

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The first implementation of a molybdenum complex with an easily accessible bis‐N‐heterocyclic carbene ligand to catalyze β‐alkylation of secondary alcohols via borrowing‐hydrogen (BH) strategy using alcohols as alkylating agents is reported. Remarkably high activity, excellent selectivity, and broad substrate scope compatibility with advantages of catalyst usage low to 0.5 mol%, a catalytic amount of NaOH as the base, and H2O as the by‐product are demonstrated in this green and step‐economical protocol. Mechanistic studies indicate a plausible outer‐sphere mechanism in which the alcohol dehydrogenation is the rate‐determining step.

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Section: Methodssupporting

confidence: 87%

Selective C‐alkylation Between Alcohols Catalyzed by N‐Heterocyclic Carbene Molybdenum

Liu

et al. 2021

Chemistry An Asian Journal

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“…The catalytic efficacy of Cp*Ir(NHC) complexes has been demonstrated for a wide variety of reactions including transfer hydrogenation of ketones and imines, [131] cross‐coupling of alcohols and amines, [132] benzylation of arenes, [133] and reductive amination [41] . In light of these reports, and recognizing that proton‐responsive complexes are suited for catalyzing hydrogen‐related reactions, the catalytic efficacy of 1 was evaluated for α ‐alkylation of ketones and β ‐alkylation of secondary alcohols using primary alcohols as alkylating agents [93–122] . Alcohols are attractive green and sustainable alkylating agents as compared to mutagenic alkyl halides and sulfonate esters employed in conventional alkylation methods [134] .…”

Section: Resultsmentioning

confidence: 99%

“…Further, NHC being a strong σ‐donor would promote the hydride transfer from the metal to a suitable substrate. The catalytic efficacy of 1 was evaluated in borrowing‐hydrogen methodology for α ‐alkylation of ketones and β ‐alkylation of secondary alcohols using primary alcohols [93–122] . Apart from this, 1 was also employed for catalytic syntheses of quinoline and lactone derivatives and selective alkylation of two steroids pregnenolone and testosterone.…”

Section: Introductionmentioning

confidence: 99%

A Proton‐Responsive Pyridyl(benzamide)‐Functionalized NHC Ligand on Ir Complex for Alkylation of Ketones and Secondary Alcohols

Kaur

Reshi

Patra

et al. 2021

Chemistry A European J

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A Cp*Ir(III) complex (1) of a newly designed ligand L 1 featuring a proton-responsive pyridyl(benzamide) appended on N-heterocyclic carbene (NHC) has been synthesized. The molecular structure of 1 reveals a dearomatized form of the ligand. The protonation of 1 with HBF 4 in tetrahydrofuran gives the corresponding aromatized complex [Cp*Ir(L 1 H)Cl]BF 4 (2). Both compounds are characterized spectroscopically and by X-ray crystallography. The protonation of 1 with acid is examined by 1 H NMR and UV-vis spectra. The proton-responsive character of 1 is exploited for catalyzing α-alkylation of ketones and β-alkylation of secondary alcohols using primary alcohols as alkylating agents through hydrogen-borrowing methodology. Compound 1 is an effec-tive catalyst for these reactions and exhibits a superior activity in comparison to a structurally similar iridium complex [Cp*Ir(L 2 )Cl]PF 6 (3) lacking a proton-responsive pendant amide moiety. The catalytic alkylation is characterized by a wide substrate scope, low catalyst and base loadings, and a short reaction time. The catalytic efficacy of 1 is also demonstrated for the syntheses of quinoline and lactone derivatives via acceptorless dehydrogenation, and selective alkylation of two steroids, pregnenolone and testosterone. Detailed mechanistic investigations and DFT calculations substantiate the role of the proton-responsive ligand in the hydrogen-borrowing process.À OH/=O, À CH 2 /=CH and À NH/ = N motifs on pyridine, [25][26][27] bipyridine, [28][29][30][31][32] bipyrimidine [33] and azole-pyridine/ pyrimidine [34][35][36][37] are particularly effective. Some of the representative examples that have been employed for catalyzing (de) hydrogenation and alkylation reactions are given in Scheme 1. Yamaguchi and co-workers reported a Cp*Ir(III) compound with

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“…Encouragingly, an array of long‐chain aliphatic alcohols such as 1‐octanol, 1‐tetradecanol and 1‐heptadecanol all furnished the respective alkylated tetrone product ( 4 k – 4 m ) in 52–68% yields. Easy synthesis of these aforementioned products is a significant improvement over the Ke's recent manganese‐carbene catalyst, [7d] where aliphatic alcohols failed to generate desired alkylated ketones. The wide substrate scope with a plethora of aliphatic primary alcohols substantiates the efficacy of our chemoselective catalyst.…”

Section: Methodsmentioning

confidence: 99%

Nickel‐Catalyzed Selective Synthesis of α‐Alkylated Ketones via Dehydrogenative Cross‐Coupling of Primary and Secondary Alcohols

2021

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Herein, we describe an isolable, airstable, homogeneous, nickel catalyst that performs dehydrogenative cross-coupling reaction between secondary and primary alcohols to result α-alkylated ketone products selectively. The sequence of steps involve in this one-pot reaction is dehydrogenation of both alcohols, condensation between the ketone and the aldehyde, and hydrogenation of the in situgenerated α,β-unsaturated ketone. Preliminary mechanistic investigation hints a radical mechanism following borrowing hydrogen reaction.

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Sustainable and Selective Alkylation of Deactivated Secondary Alcohols to Ketones by Non‐bifunctional Pincer N‐heterocyclic Carbene Manganese

Cited by 54 publications

References 101 publications

Selective C‐alkylation Between Alcohols Catalyzed by N‐Heterocyclic Carbene Molybdenum

Selective C‐alkylation Between Alcohols Catalyzed by N‐Heterocyclic Carbene Molybdenum

A Proton‐Responsive Pyridyl(benzamide)‐Functionalized NHC Ligand on Ir Complex for Alkylation of Ketones and Secondary Alcohols

Nickel‐Catalyzed Selective Synthesis of α‐Alkylated Ketones via Dehydrogenative Cross‐Coupling of Primary and Secondary Alcohols

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