Sunlight photocatalyzed regioselective β-alkylation and acylation of cyclopentanones

Transition metal-catalyzed C-H functionalization has evolved into a prominent and indispensable tool in organic synthesis. While nitrogen, phosphorus and sulfur-based functional groups (FGs) are widely employed as effective directing groups (DGs) to control the site-selectivity of C-H activation, the use of common FGs (e.g. ketone, alcohol and amine) as DGs has been continuously pursued. Ketones are an especially attractive choice of DGs and substrates due to their prevalence in various molecules and versatile reactivity as synthetic intermediates. Over the last two decades, transition metal-catalyzed C-H functionalization that is directed or mediated by ketones has experienced vigorous growth. This review summarizes these advancements into three major categories: use of ketone carbonyls as DGs, direct β-functionalization, and α-alkylation/alkenylation with unactivated olefins and alkynes. Each of these subsections is discussed from the perspective of strategic design and reaction discovery.

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“…80 Using tetrabutylammonium decatungstate (TBADT) as the catalyst (27)). 80 Using tetrabutylammonium decatungstate (TBADT) as the catalyst (27)).…”

Section: Carbon-heteroatom (C-x) Bond Formationmentioning

confidence: 99%

Transition metal-catalyzed ketone-directed or mediated C–H functionalization

et al. 2015

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“…49 We became curious about the effect imparted by a given functionality on an alkane scaffold in terms of site-selectivity in the CH cleavage reaction promoted by TBADT. 5 Consequently, we were able to find notable site-selectivity for a variety of ketones, 6,7 esters, 7 nitriles, 8 and alkylpyridines, 9 in which the S H 2 (bimolecular homolytic substitution) transition states between CH bond and decatungstate anion are highly influenced by radical polar and steric effects, rendering the functionalization of C(sp 3 )H bonds site-selective in each case. For example, β-selective CH to CC conversion of 3,3-dimethylcyclohexanone was achieved using TBADT as a photocatalyst (Scheme 1), 7 in which the lack of any α-CH functionalization was rationalized by the mismatched polar S H 2 transition state for α-CH cleavage, while the lack of γ-CH functionalization was due to the steric hindrance by the two methyl groups attached at the adjacent carbon of the targeted methylene group.…”

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confidence: 92%

Site-selectivity in TBADT-photocatalyzed C(sp³)–H Functionalization of Saturated Alcohols and Alkanes

et al. 2018

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Site-selectivity in C(sp 3 )H functionalization of aliphatic alcohols and alkanes was studied using the decatungstate anion as a photocatalyst. In the case of aliphatic alcohols, CH bond α to the hydroxy group was preferentially functionalized. The α-site-selectivity is rationalized by polar effects imparted by the hydroxy group in the S H 2 transition states. In contrast, CH functionalization of alkanes was largely affected by steric effects.

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“…[13] Organic dyes, for example, the cheap fluoresceins, display similar photocatalytic activity in some reactions [14] and seemed more appropriate as no interference by the presence of carbon monoxide is known. [15] Furthermore, CO only exhibits absorptions in the vacuum-UV range below 180 nm. [16] Our initial studies on the proposed photocatalytic carbonylation with 4-methoxybenzenediazonium tetrafluoroborate (1 a) in methanol were carried out under reaction conditions that were reported for related photoredox Meerwein reactions.…”

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confidence: 99%

Metal‐Free Carbonylations by Photoredox Catalysis

2014

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The synthesis of benzoates from aryl electrophiles and carbon monoxide is a prime example of a transition-metal-catalyzed carbonylation reaction which is widely applied in research and industrial processes. Such reactions proceed in the presence of Pd or Ni catalysts, suitable ligands, and stoichiometric bases. We have developed an alternative procedure that is free of any metal, ligand, and base. The method involves a redox reaction driven by visible light and catalyzed by eosin Y which affords alkyl benzoates from arene diazonium salts, carbon monoxide, and alcohols under mild conditions. Tertiary esters can also be prepared in high yields. DFT calculations and radical trapping experiments support a catalytic photoredox pathway without the requirement for sacrificial redox partners.

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Sunlight photocatalyzed regioselective β-alkylation and acylation of cyclopentanones

Abstract: Visible light induced direct β-C–H/C–C conversion of cyclopentanones was accomplished by using tetrabutylammonium decatungstate, TBADT, as the photocatalyst.

Cited by 131 publications

References 49 publications

Transition metal-catalyzed ketone-directed or mediated C–H functionalization

Transition metal-catalyzed ketone-directed or mediated C–H functionalization

Site-selectivity in TBADT-photocatalyzed C(sp³)–H Functionalization of Saturated Alcohols and Alkanes

Metal‐Free Carbonylations by Photoredox Catalysis

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Sunlight photocatalyzed regioselective β-alkylation and acylation of cyclopentanones

Abstract: Visible light induced direct β-C–H/C–C conversion of cyclopentanones was accomplished by using tetrabutylammonium decatungstate, TBADT, as the photocatalyst.

Cited by 131 publications

References 49 publications

Transition metal-catalyzed ketone-directed or mediated C–H functionalization

Transition metal-catalyzed ketone-directed or mediated C–H functionalization

Site-selectivity in TBADT-photocatalyzed C(sp3)–H Functionalization of Saturated Alcohols and Alkanes

Metal‐Free Carbonylations by Photoredox Catalysis

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Site-selectivity in TBADT-photocatalyzed C(sp³)–H Functionalization of Saturated Alcohols and Alkanes