Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis

Ho, Hung‐An; Manna, Kuntal; Sadow, Aaron D.

doi:10.1002/ange.201203556

Cited by 22 publications

(8 citation statements)

References 51 publications

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“…As shown in Table 2, we were delighted to find that a variety of alcohols can be applied in this fragment coupling transformation to construct C−C bonds through the extrusion of one molecule of formaldehyde, demonstrating a practical strategy utilizing abundant alcohol feedstocks directly as robust surrogates for organometallic reagents in 1,4-additions. This transformation displayed good functionality tolerance, with a variety of commonly encountered functionalities, such as ether (19), ester (20), amide (21,31), heterocycle (30,34,35), alkene (33), and ketal (34,35) being left unscathed in this reaction. Different substitution patterns at the β-position of the hydroxyl group, which would affect the nucleophilicity of the carboncentered radicals, could be accommodated, regardless of linear or cyclic, irrespective of primary, second, or tertiary.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

“…Moreover, estab- lished transformations typically lead to alkane products. 31,32 Remarkably, the Dong group recently reported a Rh-catalyzed oxidative dehydroxymethylation that could convert alcohols into synthetically valuable alkenes with high efficiency (Figure 1B). 35 Employing an electron-deficient olefin as the efficient acceptor for transfer hydrogenation, excellent efficiencies and selectivities were achieved for a broad range of alcohols.…”

Section: ■ Introductionmentioning

confidence: 99%

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Dehydroxymethylation of Alcohols Enabled by Cerium Photocatalysis

et al. 2019

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Dehydroxymethylation, the direct conversion of alcohol feedstocks as alkyl synthons containing one less carbon atom, is an unconventional and underexplored strategy to exploit the ubiquity and robustness of alcohol materials. Under mild and redox-neutral reaction conditions, utilizing inexpensive cerium catalyst, the photocatalytic dehydroxymethylation platform has been furnished. Enabled by ligand-to-metal charge transfer catalysis, an alcohol functionality has been reliably transferred into nucleophilic radicals with the loss of one molecule of formaldehyde. Intriguingly, we found that the dehydroxymethylation process can be significantly promoted by the cerium catalyst, and the stabilization effect of the fragmented radicals also plays a significant role. This operationally simple protocol has enabled the direct utilization of primary alcohols as unconventional alkyl nucleophiles for radical-mediated 1,4-conjugate additions with Michael acceptors. A broad range of alcohols, from simple ethanol to complex nucleosides and steroids, have been successfully applied to this fragment coupling transformation. Furthermore, the modularity of this catalytic system has been demonstrated in diversified radical-mediated transformations including hydrogenation, amination, alkenylation, and oxidation.

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Section: Journal Of the American Chemical Societymentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Dehydroxymethylation of Alcohols Enabled by Cerium Photocatalysis

et al. 2019

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“…According to the reported studies, 21 most of this transformation was based on metal catalysts, even precious-metal catalysts, such as Cu, 24−26 Ru, 27 Au, 28 and Pd. 29 Despite these metal catalysts have made noteworthy progress, exhibiting good yields and selectivity, there still being several key challenges, such as cost problems and poor reusability, 30 the purification of metal contaminants in the ultimate products.…”

Section: ■ Introductionmentioning

confidence: 99%

Synergetic Effect of B and O Dopants for Aerobic Oxidative Coupling of Amines to Imines

Zhai

Chu

Xie

et al. 2018

ACS Sustainable Chem. Eng.

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Boron-doped mesoporous carbon material (B–C) was fabricated by annealing boric acid and sustainable cellulose at high temperature in inert atmosphere. This heteroatom-doped carbon exhibited excellent catalytic activity and high selectivity in the oxidative coupling of amine to imines. Owing to the recyclable utilization of boric acid involved in the preparation of B–C and a kind of earth abundant natural biomass being the carbon source, this metal-free carbon catalyst could be regarded as a kind of green and sustainable catalyst. Characterizations, such as X-ray photoelectron spectroscopy and X-ray absorption near edge structure, demonstrated that boron mainly existed in the form of CBO2 and functioned as catalytic active site. A proposed catalytic mechanism based on density functional theory calculations pointed out that synergistic effect of B and O atoms in CBO2 promoted adsorption and dehydrogenation of benzylamine. The intermediators, such as hydrogen peroxide, ammonia, and phenylmethanimine, could be captured by hexamethyldisilazane, indicating rationality of the proposed mechanism. This study not only developed a new catalytic system for the transformation of amine to imine, but also broadened the application of B-doped carbon materials.

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“…Quinuclidine 17 obtained in this way represented aplausible precursor towards both quinine (1)a nd quinidine (2)i n accordance with our proposed synthetic blueprint (Figure 1c, mode "a"o r" b"c leavage). Thus,r emoval of the hydroxymethylene appendage in 17 (mode "a"c leavage,S wern oxidation;t hen rhodium-catalyzed deformylation) [10] followed by electrophilic oxygenation [1f, 11] completed the stereoselective synthesis of quinine (1)f rom alcohol 12.…”

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confidence: 99%

A Local‐Desymmetrization‐Based Divergent Synthesis of Quinine and Quinidine

Lee

Chen

2018

Angewandte Chemie

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Herein we report an ovel synthetic entry to the legendary quinuclidine natural products quinine and quinidine.T he developed strategy is based on the use of as ymmetrical and nonstereogenic precursor to access quinine and quinidine through a" local-desymmetrization" approach,i n stark contrast conceptually to the preparation of stereodefined disubstituted piperidines (or their acyclic precursors) as featured in all past syntheses.T he developed strategy also provided quinine and quinidine derivatives that could not be readily obtained through previous total syntheses or by modification of the naturally occurring substances.Quinine and quinidine are two flagship alkaloid natural products that have captivated the imaginations of generations of organic chemists,with respect to both their synthesis [1] and applications in asymmetric catalysis. [2] In the former context, although both natural products are abundant in natural and commercial supply,s ynthetic studies dedicated toward quinine and quinidine remain vibrant today more than 70 years after the landmark achievement of Woodward and Doering. [1a] On the other hand, the application of these "pseudoenantiomeric" gifts of nature in asymmetric transformations has often delivered enantiomeric products with comparable levels of optical purity,while novel analogues of quinine and quinidine continue to emerge particularly in the context of multifunctional catalysis. [3] With great appreciation for the valuable lessons from the past quinine/quinidine syntheses, [1] and as part of our continued investigations in desymmetrization-based target-oriented synthesis, [4] we embarked on ar esearch program aimed at the development of an ovel and divergent strategy for both quinine and quinidine and designed analogues.Upon cursory examination, ac ommon feature shared by the past quinine/quinidine syntheses is the early preparation of astereodefined disubstituted piperidine or astereocenterbearing acyclic piperidine precursor (Figure 1a). More specifically,a ll of these synthetic endeavors required thoughtful orchestration of diastereocontrol, whereby some met with more difficulties than others.W ef urther recognized that the relative stereochemical arrangement within quinine (1)a nd quinidine (2)( more precisely,q uinine and ent-quinidine) simply differs in the spatial relationship between the methoxyquinoline domain and the vinyl substituent ("syn"or"anti", Figure 1b). These observations prompted us to propose ah ypothetical symmetrical and nonstereogenic precursor 3 that may offer synthetic entry to both quinine (1)a nd Figure 1. a) Reported intermediates and their diastereochemical integrity in the synthesis of quinine (1)a nd quinidine (2); b) structural comparison between quinine (1)a nd quinidine( 2); c) proposed divergent synthetic strategy towards quinine (1)and quinidine (2) based on a"local-desymmetrization" approach. Bz = benzoyl, TBS = tert-butyldimethylsilyl, TBDPS = tert-butyldiphenylsilyl, Teoc = 2-(trimethysilyl)ethyloxycarbonyl.

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Acceptorless Photocatalytic Dehydrogenation for Alcohol Decarbonylation and Imine Synthesis

Cited by 22 publications

References 51 publications

Dehydroxymethylation of Alcohols Enabled by Cerium Photocatalysis

Dehydroxymethylation of Alcohols Enabled by Cerium Photocatalysis

Synergetic Effect of B and O Dopants for Aerobic Oxidative Coupling of Amines to Imines

A Local‐Desymmetrization‐Based Divergent Synthesis of Quinine and Quinidine

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