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Abstract Main‐group element‐mediated C−H activation remains experimentally challenging and the development of clear concepts and design principles has been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(pyCDC)Sb][NTf2]3(1) (pyCDC=bis‐pyridyl carbodicarbene; NTf2=bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6‐di‐tert‐butylpyridine to enable C(sp3)−H bond breaking to generate the stiba‐methylene nitrile complex [(pyCDC)Sb(CH2CN)][NTf2]2(2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction. Computational studies suggest that C−H activation proceeds via a mechanism in which acetonitrile first coordinates to the Sb center through the nitrogen atom in a κ1fashion, thereby weakening the C−H bond which can then be deprotonated by base in solution. Further, we show that1reacts with terminal alkynes in the presence of 2,6‐di‐tert‐butylpyridine to enable C(sp)−H bond breaking to form stiba‐alkynyl adducts of the type [(pyCDC)Sb(CCR)][NTf2]2(3 a–f). Compound1shows excellent specificity for the activation of the terminal C(sp)−H bond even across alkynes with diverse functionality. The resulting stiba‐methylene nitrile and stiba‐alkynyl adducts react with elemental iodine (I2) to produce iodoacetonitrile and iodoalkynes, while regenerating an Sb trication.
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Cascade Reactions of Alkynyl Ketones and Amides to Generate Unsaturated Oxacycles and Aromatic Carbocycles
Abstract We describe novel amine‐mediated transformation of alkynyl ketones and amides to generate 2‐methylene‐2H‐pyrans, substituted 3‐hydroxy‐9H‐fluoren‐9‐ones, and amine‐incorporated arenes. These cascade processes are initiated by conjugate addition of secondary amine followed by hydrolysis of the enamine/vinylogous amide intermediates. The product distribution is highly sensitive to the steric and electronic effects of the substituents on both the alkyne moieties, the tether structure connecting them, and the nature of the amine. Alkynyl amide participates in the Alder‐ene reaction favorably to generate more reactive allene amide that reacts with amine to generate amine‐incorporated arene products. These metal‐free cascade reactions are a useful synthetic method that can be exploited for the construction of various hetero‐ and carbocyclic systems.
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- Award ID(s):
- 2055055
- PAR ID:
- 10642350
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 30
- Issue:
- 65
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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