Oxalates as Activating Groups for Alcohols in Visible Light Photoredox Catalysis: Formation of Quaternary Centers by Redox-Neutral Fragment Coupling

Nawrat, Christopher C.; Jamison, Christopher R.; Slutskyy, Yuriy; MacMillan, David W. C.; Overman, Larry E.

doi:10.1021/jacs.5b07678

Cited by 343 publications

(225 citation statements)

References 32 publications

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“…[83] In contrast to the method above, the new protocol utilized cesium oxalates as the activating system to provide salts 56, which eliminated the need for a stoichiometric reductant and the added waste generated from the phthalimide group. This allowed the authors to employ an oxidative substrate activation mode, similar to that described in Scheme 12, in which the excited-state Ir III * catalyst induces oxidative fragmentation of the oxalate group through a SET event to produce a carbon radical intermediate.…”

Section: C(sp 3 )-Alcohol Derivativesmentioning

confidence: 99%

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp³)‐Substrates

Roslin

Odell

2017

Eur J Org Chem

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Over the past decade, visible-light photocatalysis has emerged as one of the brightest and most dynamic fields in modern organic chemistry. By employing a transition-metal-or organic-dye-based photocatalyst in conjunction with a low-energy visible-light source, this synthetic manifold allows the facile generation of radical intermediates that can subsequently be directed through a wide range of transformations. Although

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Section: C(sp 3 )-Alcohol Derivativesmentioning

confidence: 99%

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp³)‐Substrates

Roslin

Odell

2017

Eur J Org Chem

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“…Lastly, tertiary boronic esters were explored ( 3 nd – 3 pd ). Despite their well‐known difficulty to be efficiently engaged in metal‐catalyzed cross‐couplings,14a, 15, 19 DMAP allowed for clean activation to form quaternary carbon centers in respectable yields even from commercial and less activated t BuBpin ( 3 pd ).…”

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confidence: 99%

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

et al. 2017

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We report herein the use of a dual catalytic system comprising a Lewis base catalyst such as quinuclidin‐3‐ol or 4‐dimethylaminopyridine and a photoredox catalyst to generate carbon radicals from either boronic acids or esters. This system enabled a wide range of alkyl boronic esters and aryl or alkyl boronic acids to react with electron‐deficient olefins via radical addition to efficiently form C−C coupled products in a redox‐neutral fashion. The Lewis base catalyst was shown to form a redox‐active complex with either the boronic esters or the trimeric form of the boronic acids (boroxines) in solution.

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“…Reactions performed with isobutyric acid (2a) 10 and isopropyl oxalate (2b) 11 were unsuccessful; probably caused by the effect the required additives (K 2 HPO 4 and water) inflicted upon the N-sulfinimine, observing its hydrolysis in the crude mixture. However, under fairly anhydrous conditions, the reaction of N-(isobutyryloxy)phthalimide 2c 12 with N-sulfinimine 1a catalyzed by [Ru(bpy) 3 ] 2+ (3a) gave rise to our desired product in moderate conversion after 14 hours (entry 1, Table 1).…”

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confidence: 99%

Asymmetric radical alkylation of N-sulfinimines under visible light photocatalytic conditions

et al. 2017

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In this communication, a new photocatalytic strategy for the addition of alkyl-radical derivatives to N-sulfinimines with complete diastereoselectivity and moderate to good yields is presented. This is the first asymmetric photocatalytic addition to N-sulfinimines under visible light irradiation with smooth conditions and functional group tolerance.Enantiopure sulfinimines, or N-sulfinyl imines, have been used in the asymmetric synthesis of diverse chiral amino derivatives, e.g. a-branched amines, a-and b-amino acids, and a-and b-amino phosphonic acids.1 The N-sulfinyl group is one of the best chiral auxiliaries for imines because the CQN bond is activated for nucleophilic addition, diastereofacial selectivity is provided, and it is easily removable under mild acidic conditions. However, most reactions with N-sulfinimines employ organometallic compounds such as organolithium or Grignard reagents under very restrictive conditions (low temperature and minimal functional group tolerance). In this regard, radical reactions offer a better functional group tolerance under more suitable reaction conditions. However, only a few examples involving radical-mediated intermolecular additions to N-sulfinimines have been reported, 2-4 which are impractical because of the large amount of radical precursors and the use of toxic reagents (Bu 3 SnH). These issues are impeding a simple gateway to valuable chiral amines, and therefore a new straightforward methodology capable of overcoming these limitations is required. On the other hand, visible light photoredox catalysis has received significant attention over the past decade due to its ability to achieve bond constructions that are not possible using established procedures.5 At the same time, photoredox catalysts can also be employed to generate radicals to be used in a diverse range of proven radical strategies. This approach is based on the adeptness transition metal complexes 6 and organic dyes 7 display by engaging in SET processes following photoexcitation with visible light. Numerous photocatalytic examples of racemic radical transformations performed with imines have been published. 8 However, only one asymmetric approach has been disclosed by Ooi and co-workers (Scheme 1a). 9In Ooi's work, the addition of a-alkylamine derivatives to N-sulfonylimines to afford diamine derivatives was described. Nonetheless, no examples of visible light photocatalytic reactions with N-sulfinimines exist to the best of our knowledge. Therefore, our goal is to deliver a novel radical addition to N-sulfinimines, using photocatalysis and visible light irradiation as a viable radical-generating process, and the N-sulfinyl group as a chiral auxiliary to achieve complete stereoselectivity in the synthesis of amine derivatives (Scheme 1b).In order to achieve this goal, we performed an initial study in which the reactivity of the enantiopure N-sulfinimine 1a (R 1 = p-Tol) was tested with different radical donors (see ESI ‡Scheme 1 Previous reaction and present work of this manuscript.

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Oxalates as Activating Groups for Alcohols in Visible Light Photoredox Catalysis: Formation of Quaternary Centers by Redox-Neutral Fragment Coupling

Abstract: Alkyl oxalates are new bench-stable alcohol-activating groups for radical generation under visible light photoredox conditions. Using these precursors, the first net redox-neutral coupling of tertiary and secondary alcohols with electron-deficient alkenes is achieved.

Cited by 343 publications

References 32 publications

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp³)‐Substrates

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp³)‐Substrates

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

Asymmetric radical alkylation of N-sulfinimines under visible light photocatalytic conditions

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Oxalates as Activating Groups for Alcohols in Visible Light Photoredox Catalysis: Formation of Quaternary Centers by Redox-Neutral Fragment Coupling

Abstract: Alkyl oxalates are new bench-stable alcohol-activating groups for radical generation under visible light photoredox conditions. Using these precursors, the first net redox-neutral coupling of tertiary and secondary alcohols with electron-deficient alkenes is achieved.

Cited by 343 publications

References 32 publications

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp3)‐Substrates

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp3)‐Substrates

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

Asymmetric radical alkylation of N-sulfinimines under visible light photocatalytic conditions

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Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp³)‐Substrates

Visible‐Light Photocatalysis as an Enabling Tool for the Functionalization of Unactivated C(sp³)‐Substrates