Quantification of halogen-bonding abilities is described for a series of benzimidazolium-, imidazolium-and bis(imidazolium) halogen-bond donors (XBDs) using 31 P NMR spectroscopy. The measured Δδ( 31 P) values correlate with calculated activation free energy ΔG ‡ and catalytic activity for a Friedel−Crafts indole addition. This rapid method also serves as a sensitive indicator for Brønsted acid impurities.Letter pubs.acs.org/OrgLett
We
have established a nickel-catalyzed domino reaction that harnesses
sulfonamide, alkyl chloride, and alkyne functionalities in a multistep
sequence to afford vinylcyclopropanes bearing tetrasubstituted olefins.
The starting materials are prepared by iron-promoted aza-Prins reactions
of ynals. This method provides rapid synthetic access to valuable
building blocks with applications in medicinal chemistry. Experimental
and computational results support the initiation of the catalytic
cycle by oxidative addition of the propargylic sulfonamide, and a
key ambiphilic allenylnickel intermediate leads to a bifurcated reaction
pathway that generates olefin isomers.
Grignard reagents are commonly used as carbanion equivalents.
Herein,
we report an example of Grignard reagents acting as halide nucleophiles
to form alkyl iodides and bromides. We establish that Grignard reagents
can convert alkyl mesylates into alkyl halides, as well as be employed
in a one-pot halogenation reaction starting from alcohols, which proceed
through mesylate intermediates. The halogenation reaction is confirmed
to occur by an S
N
2 pathway with inversion of configuration
and is demonstrated to be efficient on multi-gram scale.
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