1,3,2‐Diazaphospholene‐Catalyzed Reductive Cyclizations of Organohalides**

Klett, Johannes; Woźniak, Łukasz; Cramer, Nicolai

doi:10.1002/ange.202202306

Cited by 7 publications

(1 citation statement)

References 63 publications

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“…After demonstrating that the selected boryl radical species exhibited high chemoselectivity, we next attempted to achieve stepwise dechlorinative coupling reactions with alkenes. Although some intramolecular trapping reactions of α,α-dichloro carbonyl radicals have been reported to form lactams, , intermolecular versions remain challenging and unexplored. Indeed, when 2a was treated with styrene ( 5a ) using 1a or 1b as the boryl radical precursor, the competing reduction product 3a was formed in higher yields than the coupling product 6a (Scheme b, entries 1 and 2).…”

Section: Resultsmentioning

confidence: 99%

Boryl Radicals Enabled a Three-Step Sequence to Assemble All-Carbon Quaternary Centers from Activated Trichloromethyl Groups

Zhao

Zhou

et al. 2022

J. Am. Chem. Soc.

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The construction of diversely substituted all-carbon quaternary centers has been a longstanding challenge in organic synthesis. Methods that add three alkyl substituents to a simple C(sp3) atom rely heavily on lengthy multiple processes, which usually involve several preactivation steps. Here, we describe a straightforward three-step sequence that uses a range of readily accessible activated trichloromethyl groups as the carbon source, the three C–Cl bonds of which are selectively functionalized to introduce three alkyl chains. In each step, only a single C–Cl bond was cleaved with the choice of an appropriate Lewis base–boryl radical as the promoter. A vast range of diversely substituted all-carbon quaternary centers could be accessed directly from these activated CCl3 trichloromethyl groups or by simple derivatizations. The use of different alkene traps in each of the three steps enabled facile collections of a large library of products. The utility of this strategy was demonstrated by the synthesis of variants of two drug molecules, whose structures could be easily modulated by varying the alkene partner in each step. The results of kinetic and computational studies enabled the design of the three-step reaction and provided insights into the reaction mechanisms.

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Section: Resultsmentioning

confidence: 99%

Boryl Radicals Enabled a Three-Step Sequence to Assemble All-Carbon Quaternary Centers from Activated Trichloromethyl Groups

Zhao

Zhou

et al. 2022

J. Am. Chem. Soc.

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Diazaphospholene‐Catalyzed Radical Reactions from Aryl Halides**

et al. 2022

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Diazaphospholenes are widely used as hydride transfer catalysts, however their use in radical reactions is a recently emerging area. Here, we show prior stoichiometric radical cyclizations of aryl iodides mediated by diazaphospholene hydrides are made catalytic by the combination of phenylsilane and alkali metal salts to regenerate the diazaphospholene hydride. The scope was expanded to include aryl bromides, which benefit from visible light irradiation. Twenty one substrates underwent cyclization, including a dearomative cyclization. Extension to six intermolecular radical hydroarylations with arenes, thiophenes, and a pyridine was also accomplished.

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Reductive Asymmetric Aza‐Mislow‐Evans Rearrangement by 1,3,2‐Diazaphospholene Catalysis**

Zhang

Cramer

2023

Angewandte Chemie

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1,3,2‐diazaphospholene hydrides (DAP−H) enable smooth conjugate reduction of polarized double bonds. The transiently formed phosphorus‐enolate provides a potential platform for reductive α‐functionalizations. In this respect, asymmetric C‐heteroatom bond forming processes are synthetically appealing but remain elusive. We report a 1,3,2‐diazaphospholene‐catalyzed three‐step cascade reaction of N‐sulfinyl acrylamides comprised of conjugate reduction, [2,3]‐sigmatropic aza‐Mislow‐Evans rearrangement and subsequent S−O bond cleavage. The obtained enantio‐enriched α‐hydroxy amides are formed in good yields and excellent enantiospecificity. The stereo‐defined P‐bound N,O‐ketene aminal ensures an excellent transfer of chirality from the sulfur stereocenter to α‐carbon. The transformation operates under mild conditions at ambient temperature. Moreover, DAP−H is a competent reductant for the cleavage of formed sulfenate ester, eliminating the extra step in traditional Mislow‐Evans processes.

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1,3,2‐Diazaphospholene‐Catalyzed Reductive Cyclizations of Organohalides**

Cited by 7 publications

References 63 publications

Boryl Radicals Enabled a Three-Step Sequence to Assemble All-Carbon Quaternary Centers from Activated Trichloromethyl Groups

Boryl Radicals Enabled a Three-Step Sequence to Assemble All-Carbon Quaternary Centers from Activated Trichloromethyl Groups

Diazaphospholene‐Catalyzed Radical Reactions from Aryl Halides**

Reductive Asymmetric Aza‐Mislow‐Evans Rearrangement by 1,3,2‐Diazaphospholene Catalysis**

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