Dirhodium(II) Caprolactamate:  An Exceptional Catalyst for Allylic Oxidation

Catino, Arthur J.; Forslund, Raymond E.; Doyle, Michael P.

doi:10.1021/ja045330o

Cited by 227 publications

(160 citation statements)

References 22 publications

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“…Unlike previous TBHP oxidations of 1-substituted cyclohexenes, from which the dominant product resulted from oxidation at the 3-position,5–9 the dominant product of the oxidation of ( R )-(+)-limonene was racemic carvone ( 16 , 44 % isolated yield). The observed carvone 16 arose from hydrogen atom abstraction from the 6-position of limonene to produce a racemic free radical that underwent subsequent transformation.…”

Section: Resultsmentioning

confidence: 69%

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

et al. 2008

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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.

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Section: Resultsmentioning

confidence: 69%

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

et al. 2008

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“…For example, established methods for allylic oxidation via reactive radical species (e.g. Pd(OH) 2 /C/ t -BuOOH (42) or Rh 2 (cap) 4 / t -BuOOH (43)) were unfruitful due to competitive functionalization of the C1–C12 olefin (i.e. epoxidation, 1,2-difunctionalization).…”

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confidence: 99%

A 15-step synthesis of (+)-ryanodol

Chuang

Reisman

2016

Science

109

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Abstract(+)-Ryanodine and (+)-ryanodol are complex diterpenoids that modulate intracellular Ca 2+ release at ryanodine receptors, ion channels critical for skeletal and cardiac muscle excitation-contraction coupling and synaptic transmission. Chemical derivatization of these diterpenoids has demonstrated that certain peripheral structural modifications can alter binding affinity and selectivity among ryanodine receptor isoforms. Here we report a short chemical synthesis of (+)-ryanodol that proceeds in only 15 steps from the commercially available terpene (S)-pulegone. The efficiency of the synthesis derives from the use of a Pauson-Khand reaction to rapidly build the carbon framework, and a remarkable SeO 2 -mediated oxidation to install three oxygen atoms in single step. This work highlights how strategic C-O bond constructions can streamline the synthesis of poly-hydroxylated terpenes by minimizing protecting group and redox adjustments.Terpenes are a large and structurally diverse family of natural products that range from simple hydrocarbons associated with flavors and fragrances, to complex, highly oxidized polycyclic molecules such as the anti-malarial drug artemisinin, and the anticancer compounds ingenol and taxol (1). Although terpenes are isolated from natural sources, it can be challenging to translate their biological activity into a practical application (2). In some cases the hurdle is low natural abundance; other times, it is the difficulty encountered by chemists seeking to precisely edit a terpene's molecular structure in order to improve its drug-like properties or interrogate its role in modulating disease pathways. The development of concise chemical syntheses of terpenes can transform our ability to use these molecules and their synthetic derivatives as biological probes or as lead compounds for the development of new medicines (3-5). Furthermore, these scientific efforts often innovate chemical reactivity or synthetic design concepts (6).The natural product ryanodine (1) (7,8) and its hydrolysis product ryanodol (2) (8,9) are among the most highly oxidized and synthetically challenging diterpenoids reported to date (Fig 1-A). Isolated from the tropical shrub Ryania speciosa Vahl in connection with its insecticidal properties (7), ryanodine is the namesake ligand of the ryanodine receptors (RyRs) (10), an important family of ion channels that regulate intracellular Ca 2+ release and play a critical role in signal transduction (11). In mammalian cells, these receptors exist in multiple isoforms (RyR1, RyR2, and RyR3) that serve to mediate both movement and cognitive function. Mutations of RyRs are associated with genetic diseases such as * To whom correspondence should be addressed: reisman@caltech.edu. ‡ These authors contributed equally. Since the initial reports describing the isolation of ryanodine from Ryania, a number of congeners (known as ryanoids) that vary in oxidation pattern have been isolated (16)(17)(18)(19)(20). Whereas ryanodol -the compound obtained by hydrolysis of ryanodin...

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“…In this case the system O 2 /TEMPO is used as a catalyst for the cleavage process, but the reaction also proceeds without the addition of TEMPO, though with lower yields [29]. Recently, communications appeared related to similar oxidation processes with participation of rhodium catalysts [30–33]. …”

Section: Resultsmentioning

confidence: 99%

Unusual reactions of diazocarbonyl compounds with α,β-unsaturated δ-amino esters: Rh(II)-catalyzed Wolff rearrangement and oxidative cleavage of N–H-insertion products

Nikolaev

Medvedev

Galkina

et al. 2016

Beilstein J. Org. Chem.

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SummaryRh(II)-сatalyzed reactions of aroyldiazomethanes, diazoketoesters and diazodiketones with α,β-unsaturated δ-aminoesters, in contrast to reactions of diazomalonates and other diazoesters, give rise to the Wolff rearrangement and/or oxidative cleavage of the initially formed N–H-insertion products. These oxidation processes are mediated by Rh(II) catalysts possessing perfluorinated ligands. The formation of pyrrolidine structures, characteristic for catalytic reactions of diazoesters, was not observed in these processes at all.

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Dirhodium(II) Caprolactamate: An Exceptional Catalyst for Allylic Oxidation

Cited by 227 publications

References 22 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 15-step synthesis of (+)-ryanodol

Unusual reactions of diazocarbonyl compounds with α,β-unsaturated δ-amino esters: Rh(II)-catalyzed Wolff rearrangement and oxidative cleavage of N–H-insertion products

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