Triarylborane-Catalyzed Reductive <i>N</i>-Alkylation of Amines: A Perspective

Hoshimoto, Yoichi; Ogoshi, Sensuke

doi:10.1021/acscatal.9b01356

Cited by 44 publications

(15 citation statements)

References 77 publications

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“…The N -alkylation of amines through carbon–nitrogen bond formation has become an efficient approach for the construction of a plethora of N -alkylamines, which are essential motifs in pharmaceuticals, agrochemicals, and natural products (Figure a) . Among the state-of-the-art synthetic methods, the traditional protocols involved a noncatalytic reaction of amines with alkyl halides, tosylates, or triflates, which are limited due to their toxicity, poor chemoselectivity, overalkylation, and generation of stoichiometric waste .…”

Section: Introductionmentioning

confidence: 99%

Boron-Catalyzed N-Alkylation of Arylamines and Arylamides with Benzylic Alcohols

2019

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A sustainable boron-based catalytic approach for chemoselective N-alkylation of primary and secondary aromatic amines and amides with primary, secondary, and tertiary benzylic alcohols has been presented. The metal-free protocol operates at low catalyst loading, tolerates several functional groups, and generates H2O as the sole byproduct. Preliminary mechanistic studies were performed to demonstrate the crucial role of boron catalyst for the activation of the intermediate dibenzyl ether and to identify the rate-determining step.

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Section: Introductionmentioning

confidence: 99%

Boron-Catalyzed N-Alkylation of Arylamines and Arylamides with Benzylic Alcohols

2019

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“…The remarkable success of main-group Lewis acids (LAs) in general, and electron-deficient triarylboranes (BAr 3 ) such as B(C 6 F 5 ) 3 in particular, is clearly evident in the wide variety of chemical transformations they have been applied to, many of them associated with the concept of “frustrated” Lewis pairs (FLPs) . Striking examples include hydrogenation, hydrosilylation, CO 2 reduction, defunctionalization, C–H bond activation, and Lewis pair (LP) polymerization . Although these reactions no longer require the use of costly, scarce, and oftentimes toxic transition-metal catalysts, as homogeneous catalysts the boranes cannot be easily recycled and require separation from the products.…”

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confidence: 99%

ROMP-Boranes as Moisture-Tolerant and Recyclable Lewis Acid Organocatalysts

et al. 2020

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Although widely used in catalysis, the multistep syntheses and high loadings typically employed are limiting broader implementation of highly active tailor-made arylborane Lewis acids and Lewis pairs. Attempts at developing recyclable systems have thus far met with limited success, as general and versatile platforms are yet to be developed. We demonstrate a novel approach that is based on the excellent control and functional group tolerance of ring-opening metathesis polymerization (ROMP). The ROMP of highly Lewis acidic borane-functionalized phenylnorbornenes afforded both a soluble linear copolymer and a cross-linked organogel. The polymers proved highly efficient as recyclable catalysts in the reductive N-alkylation of arylamines under mild conditions and at exceptionally low catalyst loadings. The modular design presented herein can be readily adapted to other finely tuned triarylboranes, enabling wide applications of ROMP-borane polymers as well-defined supported organocatalysts.

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“…One possibility is that the carbene carbon atom works as a Lewis base (path I; the right path in Fig. 5b) [1][2][3][4][5][6][7][8][9]35,36 , while the other is that the Nphosphinoyl oxygen functions as a Lewis base (path II; the left path in Fig. 5b) 37 .…”

Section: Resultsmentioning

confidence: 99%

“…T here have been many recent developments in the chemistry of frustrated Lewis pairs (FLPs) that have been of note, for example, the activation of H 2 mediated by main-group elements [1][2][3][4][5][6][7][8][9] . In general, FLPs are transient and not shelf-stable species making their isolation challenging.…”

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confidence: 99%

A boron-transfer mechanism mediating the thermally induced revival of frustrated carbene–borane pairs from their shelf-stable adducts

et al. 2021

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Chemists have designed strategies that trigger the conformational isomerization of molecules in response to external stimuli, which can be further applied to regulate the complexation between Lewis acids and bases. We have recently developed a system in which frustrated carbene–borane pairs are revived from shelf-stable but external-stimuli-responsive carbene–borane adducts comprised of N-phosphine-oxide-substituted imidazolylidenes (PoxIms) and triarylboranes. Herein, we report the detailed mechanism on this revival process. A thermally induced borane-transfer process from the carbene carbon atom to the N-phosphinoyl oxygen atom initiates the transformation of the carbene–borane adduct. Subsequent conformational isomerization via the rotation of the N-phosphinoyl group in PoxIm moieties eventually leads to the revival of frustrated carbene–borane pairs that can cleave H2. We believe that this work illustrates an essential role of dynamic conformational isomerization in the regulation of the reactivity of external-stimuli-responsive Lewis acid-base adducts that contain multifunctional substituents.

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Triarylborane-Catalyzed Reductive N-Alkylation of Amines: A Perspective

Cited by 44 publications

References 77 publications

Boron-Catalyzed N-Alkylation of Arylamines and Arylamides with Benzylic Alcohols

Boron-Catalyzed N-Alkylation of Arylamines and Arylamides with Benzylic Alcohols

ROMP-Boranes as Moisture-Tolerant and Recyclable Lewis Acid Organocatalysts

A boron-transfer mechanism mediating the thermally induced revival of frustrated carbene–borane pairs from their shelf-stable adducts

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