Optimal TBHP Allylic Oxidation of Δ<sup>5</sup>-Steroids Catalyzed by Dirhodium Caprolactamate

Choi, Hojae; Doyle, Michael P.

doi:10.1021/ol7025284

Cited by 71 publications

(38 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The alkylperoxy radical either abstracts a hydrogen atom from the allylic position of another hydrocarbon to form hydroperoxide or undergoes oxidation of Rh 2 4+ to form the enone product directly. This direct conversion explains why alcohols are either not observed9 or are generally very minor products in TBHP oxidations that are catalyzed by Rh 2 (cap) 4 10. This pathway provides a viable alternative to bimolecular disproportionation of two peroxy radicals that would form an alcohol and a ketone in equivalent amounts along with dioxygen (the Russell mechanism) 39.…”

Section: Resultsmentioning

confidence: 96%

“…Initial oxidation occurs between TBHP and Rh 2 (cap) 4 to form the oxidized dirhodium(II,III) intermediate and the tert -butoxy radical that, in turn, abstracts a hydrogen atom from TBHP at a rate that is much faster than hydrogen atom abstraction from the allylic position of the alkene 29,30. The tert -butylperoxy radical undergoes selective hydrogen atom abstraction from the hydrocarbon substrate: a process that is well documented and universally accepted 9, 10,31,32. The existence of an allylic radical in these reactions is also consistent with the conversion of optically pure limonene into racemic carvone (eq 3).…”

Section: Resultsmentioning

confidence: 99%

“…Although the tert -butylperoxy radical is the most likely hydrogen abstraction agent,8–10 the possibility of oxo-metal involvement, especially with ruthenium catalysts,21 persists. For that reason, having a model system able to distinguish between these mechanistic pathways would provide a better understanding of this oxidative process.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

et al. 2008

Self Cite

View full text Add to dashboard Cite

Dirhodium(II) caprolactamate exhibits optimal efficiency for the production of the tert-butylperoxy radical, which is a selective reagent for hydrogen atom abstraction. These oxidation reactions occur with aqueous tert-butyl hydroperoxide (TBHP) without rapid hydrolysis of the caprolactamate ligands on dirhodium. Allylic oxidations of enones yield the corresponding enedione in moderate to high yields, and applications include allylic oxidations of steroidal enones. Although methylene oxidation to a ketone is more effective, methyl oxidation to a carboxylic acid can also be achieved. The superior efficiency of dirhodium(II) caprolactamate as a catalyst for allylic oxidations by TBHP (mol % catalyst, % conversion) is described in comparative studies with other metal catalysts that are also reported to be effective for allylic oxidations. That different catalysts produce essentially the same mixture of products with the same relative yields suggests that the catalyst is not involved in product forming steps. Mechanistic implications arising from studies of allylic oxidation with enones provide new insights into factors that control product formation. A previously undisclosed disproportionation pathway, catalyzed by the tert-butoxy radical, of mixed peroxides for the formation of ketone products via allylic oxidation has been uncovered.

show abstract

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

et al. 2008

Self Cite

View full text Add to dashboard Cite

show abstract

“…Indeed, tert-butoxide and tert-butyl peroxy radicals are formed through degradation of TBHP by catalysts. Those radicals then oxidize steroidal compounds [19,20,[26][27][28][29][30][31][32][33]36].…”

Section: Reported Methodsmentioning

confidence: 99%

A Short Review of Methods for the Allylic Oxidation of Δ5 Steroidal Compounds to Enones

Sg¹,

Jp²

2016

J Steroids Horm Sci

View full text Add to dashboard Cite

Introduction of α, β-unsaturated ketones to ∆ 5 steroidal olefins changes the characteristics and biological function of those compounds. Several synthetic methods have been reported to accomplish carbonyl introduction to ∆ 5 steroidal olefins. Herein, this short review will catalogue many of those oxidative methods, particularly those proceeding through a peroxide intermediate and/or use chromium complexes as reagents. to undesired side products, one in particular being C25 for steroids with side chains [15]. Furthermore, cleavage of the side chain can occur concurrent with allylic oxidation [16].Protecting the C3 hydroxy group is commonly accomplish by esterification using acetic anhydride to make cholesteryl acetate. The authors of this review prefer esterification with benzoyl chloride since cholesteryl benzoate products can be more easily isolated with recrystallization in acetone and water than the steroidal acetates. This esterification is necessary because many oxidants and catalysts will convert the C3 hydroxyl group to a ketone [17].Due to interest in "green" or environmentally benign chemistry, chemists have questioned the ethics of earlier catalysts. Environmental and health concerns have motivated the search for new oxidants and catalysts [18]. From chromium based catalysts, the next phase in steroidal allylic oxidation manifested through more environmentally friendly metallic catalysts that use TBHP as an oxygen donor. Meanwhile, several methods have been reported to give steroidal oxidation without any metal catalysts using as sodium chlorite and sodium hypochlorite [19,20]. Additionally, recoverable heterogeneous catalysts, clay

show abstract

“…6 Here, we report that dirhodium(II) caprolactamate [Rh 2 (cap) 4 ] exhibits similar oxidative reactivity toward hydroxamic acids when TBHP is the terminal oxidant; this catalytic combination in the presence of dienes provides HDA cycloadducts in high efficiency under mild reaction conditions. The present study provides the first example of the Rh 2 (cap) 4 -catalyzed oxidation of hydroxamic acids and extends the potential utility of this important catalyst, which has already been used for efficient catalytic oxidation of activated C-H bonds, [16][17][18][19][20][21][22] phenols, and anilines. 23 We began our studies by examining the reaction of hydroxamic acid 1 and 1.2 equivalents of 1,3-cyclohexadiene 3 in the presence of 1 mol% Rh 2 (cap) 4 and 1.0 equivalent of TBHP in CH 2 Cl 2 at room temperature.…”

mentioning

confidence: 91%

The Oxidative Acylnitroso Hetero-Diels-Alder Reaction Catalyzed by Dirhodium Caprolactamate

Tusun

2012

Synlett

View full text Add to dashboard Cite

An effective protocol is described for the generation and in situ Diels-Alder trapping of acylnitroso derivatives. In this procedure, the oxidation of hydroxamic acid is efficiently catalyzed by dirhodium(II) caprolactamate with tert-butyl hydroperoxide (TBHP) in the presence of dienes at room temperature. Using this approach we obtained a variety of hetero-Diels-Alder cycloadducts in yields of up to 96% at 0.1 mol% catalyst loading.

show abstract

Optimal TBHP Allylic Oxidation of Δ⁵-Steroids Catalyzed by Dirhodium Caprolactamate

Abstract: Dirhodium caprolactamate is the most efficient catalyst for the oxidation of Delta5-steroids to 7-keto-Delta5-steroids by 70% tert-butyl hydroperoxide in water (T-HYDRO). Isolated product yields range from 38 to 87%.

Cited by 71 publications

References 36 publications

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

A Short Review of Methods for the Allylic Oxidation of Δ5 Steroidal Compounds to Enones

The Oxidative Acylnitroso Hetero-Diels-Alder Reaction Catalyzed by Dirhodium Caprolactamate

Contact Info

Product

Resources

About

Optimal TBHP Allylic Oxidation of Δ5-Steroids Catalyzed by Dirhodium Caprolactamate

Abstract: Dirhodium caprolactamate is the most efficient catalyst for the oxidation of Delta5-steroids to 7-keto-Delta5-steroids by 70% tert-butyl hydroperoxide in water (T-HYDRO). Isolated product yields range from 38 to 87%.

Cited by 71 publications

References 36 publications

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

Allylic Oxidations Catalyzed by Dirhodium Caprolactamate via Aqueous tert-Butyl Hydroperoxide: The Role of the tert-Butylperoxy Radical

A Short Review of Methods for the Allylic Oxidation of Δ5 Steroidal Compounds to Enones

The Oxidative Acylnitroso Hetero-Diels-Alder Reaction Catalyzed by Dirhodium Caprolactamate

Contact Info

Product

Resources

About

Optimal TBHP Allylic Oxidation of Δ⁵-Steroids Catalyzed by Dirhodium Caprolactamate