A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new CO bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the arylboronic acid and oxalic acid.
The arylboronic acid
catalyzed dehydrative C-alkylation
of 1,3-diketones and 1,3-ketoesters using secondary benzylic alcohols
as the electrophile is reported, forming new C–C bonds (19
examples, up to 98% yield) with the release of water as the only byproduct.
The process is also applicable to the allylation of benzylic alcohols
using allyltrimethylsilane as the nucleophile (12 examples, up to
96% yield).
Gold-catalyzed hydroarylation
of unactivated alkynes with indoles
have previously been reported to proceed with double indole addition
to produce symmetrical bis(indolyl)methanes (BIMs). We demonstrate
for the first time that the selectivity of the gold-catalyzed reaction
can be fully switched to allow for isolation of the vinylindole products
instead. Furthermore, this selective reaction can be utilized to synthesize
the more difficult to access unsymmetrical BIMs from readily available
starting materials.
A mild
and inexpensive method for direct hydrodecarboxylation of
aliphatic carboxylic acids has been developed. The reaction does not
require metals, light, or catalysts, rendering the protocol operationally
simple, easy to scale, and more sustainable. Crucially, no additional
H atom source is required in most cases, while a broad substrate scope
and functional group tolerance are observed.
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