Chiral variants of
group IX Cp and Cp* catalysts are well established
and catalyze a broad range of reactions with high levels of enantioselectivity.
Enantiocontrol in these systems results from ligand design that focuses
on appropriate steric blocking. Herein we report the development of
a new planar chiral indenyl rhodium complex for enantioselective C–H
functionalization catalysis. The ligand design is based on establishing
electronic asymmetry in the catalyst, to control enantioselectivity
during the reactions. The complex is easily synthesized from commercially
available starting materials and is capable of catalyzing the asymmetric
allylic C–H amidation of unactivated olefins, delivering a
wide range of high-value enantioenriched allylic amide products in
good yields with excellent regio- and enantioselectivity. Computational
studies suggest that C–H cleavage is rate- and enantio-determining,
while reductive C–N coupling from the RhV-nitrenoid
intermediate is regio-determining.
Indoles and N-alkylindoles undergo Friedel-Crafts addition to aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate and a trialkylamine to produce 3-(1-silyloxyalkyl)indoles. Neutralization of the reaction mixture with pyridine followed by deprotection under basic conditions with tetrabutylammonium fluoride provides the 1:1 adduct as the free alcohol. This method prevents spontaneous conversion of the desired products to the thermodynamically favored bisindolyl(aryl)methanes, a process typically observed when indoles are reacted with aldehydes under acidic conditions.
N-Alkylindoles undergo Friedel −Crafts addition to aryl and secondary alkyl nitrones in the presence of trimethylsilyl trifluoromethanesulfonate and trialkylamine to produce 3-(1-(silyloxyamino)alkyl)indoles. Spontaneous conversion to bisindolyl(aryl)methanes, which is thermodynamically favored for nitrones derived from aromatic aldehydes, is suppressed under the reaction conditions. The silyloxyamino group can be deprotected with tetrabutylammonium fluoride to yield hydroxylamines. Note pubs.acs.org/joc
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