Smooth Photocatalytic Preparation of 2‐Substituted 1,3‐Benzodioxoles

Ravelli, Davide; Albini, Angelo; Fagnoni, Maurizio

doi:10.1002/chem.201002546

Cited by 65 publications

(39 citation statements)

References 56 publications

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“…Nowadays, due to its most photoactivity, highest stability, low cost and non-toxicity, TiO 2 is most probably the only photocatalyst suitable for heavy industrial applications (Hashimoto et al, 2005;Ravelli et al, 2011). In the last 30 years various research groups have developed several photocatalityc processes in which it plays a key role as catalyst.…”

Section: Applications Of Tiomentioning

confidence: 99%

“…Their preliminary studies on the oxidation of cyanide to cyanate, by using four different forms of TiO 2 under xenon lamp, opened the way for the photodegradation of environmental pollutants. In the last three decades, TiO 2 powders have known wide applications into the recovery of water of industrial, agricultural or civil origin, as well as the decontamination of atmosphere and soil, through the mineralization of the pollutants, or at least their transformation into non-toxic compounds (Fox & Dulay, 1993;Gaya & Abdullaha, 2008;Hoffmann et al, 1995;Ravelli et al, 2011). Of course, the great advantage of these photocatalytic systems depends on the fact that they do not need the use of stoichiometric quantities of chemicals, potentially themselves polluting, but they act under light (often sunlight represents the best choice) in the presence of oxygen (Malato et al, 2007).…”

Section: Photodegradation Of Pollutantsmentioning

confidence: 99%

“…7 (Kisch, 2001;Ravelli et al, 2011). An excited photocatalyst (C*) oxidizes a substrate (S) when E(C*) is more positive than the E(S), whereas there is reduction when E(C*) is lower than E(S).…”

Section: Redox Potentials Of Semiconductorsmentioning

confidence: 99%

“…The same group has recently shown that irradiated TBADT can also effectively catalyze the alkylation at position 2 of 1,3-benzodioxoles, making this moiety more biological active and enzyme-specific (Eq. 24) (Ravelli et al, 2011). …”

Section: C-c Bond Forming Reactionsmentioning

confidence: 99%

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Semiconductors in Organic Photosynthesis

Gambarotti¹,

Melone²,

Punta³

2012

Artificial Photosynthesis

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Section: Applications Of Tiomentioning

confidence: 99%

Section: Photodegradation Of Pollutantsmentioning

confidence: 99%

Section: Redox Potentials Of Semiconductorsmentioning

confidence: 99%

Section: C-c Bond Forming Reactionsmentioning

confidence: 99%

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Semiconductors in Organic Photosynthesis

Gambarotti¹,

Melone²,

Punta³

2012

Artificial Photosynthesis

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“…We used the inorganic photocatalyst tetrabutylammonium decatungstate 25 (TBADT, 5 mol%) because, upon light excitation, it can easily photogenerate a nucleophilic carbon-centred radical by homolytically cleaving the inactive methylene C-H bond in 2a 26 via a hydrogen atom transfer (HAT) mechanism. The experiments were conducted at 35 C in acetonitrile (CH3CN) and under irradiation by a single black-light-emitting diode (black LED, λmax = 365 nm).…”

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confidence: 99%

Asymmetric catalytic formation of quaternary carbons by iminium ion trapping of radicals

Murphy

Bastida

Paria

et al. 2016

Nature

Self Cite

391

159

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A central goal of modern organic chemistry is to develop novel catalytic enantioselective carbon-carbon bond-forming strategies for forging quaternary stereogenic centres. While considerable advances have been achieved in the realm of polar reactivity 1 , radical transformations have found very limited application 2 . This is despite the fact that open-shell intermediates are intrinsically primed for connecting structurally congested carbons, as their reactivity is only marginally affected by steric factors 3 . Herein we demonstrate how the combination of photoredox 4 and asymmetric organic catalysis 5 enables enantioselective radical conjugate additions to β,β-disubstituted cyclic enones to set quaternary carbon stereocentres with high fidelity. Key to our success was the design of a chiral organic catalyst, purposely adorned with a redox-active carbazole moiety, which drives the stereoselective interception of photochemically-generated carbon-centred radicals by means of an electron-relay mechanism. We demonstrate the generality of this organocatalytic radical-trapping strategy with two sets of open-shell intermediates, formed through unrelated light-triggered pathways from readily available substrates and photoredox catalysts. To the best of our knowledge, this method represents the first application of iminium ion activation 6 (a successful catalytic strategy for enantioselective polar chemistry) within the realm of radical reactivity.Organic chemists generally rely on polar reactivity to address the challenge of forging quaternary carbon stereocentres in a catalytic enantioselective fashion 1 . Of the synthetic methods available, metal-catalysed conjugate additions of organometallic nucleophilic species to trisubstituted unsaturated carbonyl substrates have recently emerged as a powerful technology [7][8][9][10][11] (Fig. 1a). These are reliable and stereoselective processes, but they generally require controlled reaction conditions and preformed organometallic reagents 7-10 . In contrast, there has been limited success in developing analogous transformations with nucleophilic carbon-centred radicals. While a few examples of metal-catalysed enantioselective radical conjugate additions have been reported [12][13][14][15] , none of these approaches provide for the formation of sterically demanding quaternary carbons. Our herein-reported work was prompted by the desire to address this gap in catalytic enantioselective methodology.Our initial motivation stems from the notion that, due to the long incipient carbon-carbon bond in the early transition state 16 , additions of radicals to electron-deficient olefins are rather insensitive to steric hindrance 3 . This makes radical reactivity particularly suited to connecting structurally complex carbon fragments while forging quaternary carbons, as testified to by literature synthesis of a natural product facilitated by radical conjugate additions 17 .

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1-Butanaminium,N,N,N-Tributyl-, Eicosa-μ-oxodi-μ5-oxodecaoxodecatungstate(4-) (4:1)

Sikervar¹

Encyclopedia of Reagents for Organic Synthesis

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Smooth Photocatalytic Preparation of 2‐Substituted 1,3‐Benzodioxoles

Cited by 65 publications

References 56 publications

Semiconductors in Organic Photosynthesis

Semiconductors in Organic Photosynthesis

Asymmetric catalytic formation of quaternary carbons by iminium ion trapping of radicals

1-Butanaminium,N,N,N-Tributyl-, Eicosa-μ-oxodi-μ5-oxodecaoxodecatungstate(4-) (4:1)

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