An Effective Method for Allylic Oxidation of Δ<sup>5</sup>-Steroids Using <i>tert</i>-Butyl Hydroperoxide

Li, Yuancheng; Wú, Xiànghóng; Lee, Tae Bum; Isbell, Eleanor K; Parish, Edward J.; Gorden, Anne E. V.

doi:10.1021/jo902637k

Cited by 27 publications

(16 citation statements)

References 28 publications

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“…A free radical mechanism is generally accepted for hydroperoxide‐ and chlorite‐mediated allylic/benzylic oxidations and a determinant step is the formation of carbon radicals which can further react to form oxygenated products ,. To confirm the reaction mechanism, an experiment was run with the conditions in Table , Entry 2, in the presence of the radical inhibitor butylated hydroxytoluene (BHT, 50 mol%).…”

Section: Resultsmentioning

confidence: 99%

“…The utility of this procedure for the semisynthesis of the naturally occurring picealactones A, B and C was next demonstrated. These picealactones were isolated from the heartwood of Picea morrisonicola Hayata and bear a 5‐dehydro‐18,6‐olide moiety common to the ent ‐kaurane stevionolide from Stevia lucida Lag . A previous report concerns their preparation from abietic acid, but their biological activity has not been investigated to date.…”

Section: Resultsmentioning

confidence: 99%

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Regioselective Benzylic Oxidation of Aromatic Abietanes: Application to the Semisynthesis of the Naturally Occurring Picealactones A, B and C

et al. 2017

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Oxygenated aromatic abietanes are an important class of naturally occurring compounds in plants where they play specific ecological roles. However, limited availability from their natural sources hampers their exploitation for the development of new drugs to treat human diseases. Herein the benzylic oxidation of aromatic abietanes mediated by sodium chlorite and aqueous tert‐butyl hydroperoxide is reported. The method is regioselective for 12‐substituted derivatives and gives the 7‐oxo products, in good yields. Moreover, it conveniently replaces the use of toxic chromium reagents for this transformation. Preparation of 7‐oxo, 7‐oxo‐15‐hydroperoxy and 7‐oxo‐15‐hydroxy derivatives of other aromatic abietanes is also possible with this method. Furthermore, the reaction products were used as key intermediates for a short and facile semisynthesis of the naturally occurring picealactones A, B and C to disclose their anti‐proliferative activity for the first time.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Regioselective Benzylic Oxidation of Aromatic Abietanes: Application to the Semisynthesis of the Naturally Occurring Picealactones A, B and C

et al. 2017

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“…118 The protocol gave only moderate yields of enones, but was later optimized by Nikolaropoulos with respect to the phase-transfer catalyst and repeated addition of low quantities of the cooxidant providing good yields and easy workup ( tolerant of a wide range of functional groups such as hydroxyl groups and halogen substituents and is not sensitive to air and water (Scheme 21). 119…”

Section: Copper Reagentsmentioning

confidence: 99%

Allylic Oxidations of Olefins to Enones

Weidmann

Maison

2013

Synthesis

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Allylic oxidations of olefins to enones are C-H functionalizations and are valuable organic transformations that permit the synthesis of value-added products from simple precursors. A variety of stoichiometric and catalytic metal-based methods are available for these conversions. In addition, metal-free and biocatalytic protocols are gaining in importance. This review summarizes the available oxidation methods and compares their regio-and chemoselectivities.

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“…Resonance originating from C7 oxidation is more energetically favored than resonance originating from C4 oxidation due to delocalization to the tertiary C5 carbon rather than to the secondary C6 carbon. It was calculated that radical oxidation at C7 is favored by -4.65 kcal/ mol over C4 on a two ring system containing the A and B ring moiety of cholesterol [11] (Figure 1). It should be noted as an exception that selenium complexes have been reported to oxidize C4 rather than C7 [12,13].…”

Section: Introductionmentioning

confidence: 99%

“…Perhaps this explains why the oxidative methods surveyed in Tables 1-5 occur exclusively through a radical mechanism. With respect to the radical mechanism, it is important to note that tertiary carbons are present on steroidal compounds that can be radically oxidized leading C4 and C7 resonance demonstrated by a two ring system with a similar moiety [11].…”

Section: Introductionmentioning

confidence: 99%

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

Sg¹,

Jp²

2016

J Steroids Horm Sci

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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

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An Effective Method for Allylic Oxidation of Δ⁵-Steroids Using tert-Butyl Hydroperoxide

Cited by 27 publications

References 28 publications

Regioselective Benzylic Oxidation of Aromatic Abietanes: Application to the Semisynthesis of the Naturally Occurring Picealactones A, B and C

Regioselective Benzylic Oxidation of Aromatic Abietanes: Application to the Semisynthesis of the Naturally Occurring Picealactones A, B and C

Allylic Oxidations of Olefins to Enones

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

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An Effective Method for Allylic Oxidation of Δ5-Steroids Using tert-Butyl Hydroperoxide

Cited by 27 publications

References 28 publications

Regioselective Benzylic Oxidation of Aromatic Abietanes: Application to the Semisynthesis of the Naturally Occurring Picealactones A, B and C

Regioselective Benzylic Oxidation of Aromatic Abietanes: Application to the Semisynthesis of the Naturally Occurring Picealactones A, B and C

Allylic Oxidations of Olefins to Enones

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

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An Effective Method for Allylic Oxidation of Δ⁵-Steroids Using tert-Butyl Hydroperoxide