Bis(amidate)bis(amido) Titanium
Complex: A Regioselective Intermolecular Alkyne Hydroamination Catalyst
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Abstract
An
efficient and selective bis(amidate)bis(amido) titanium precatalyst
for the anti-Markovnikov hydroamination of alkynes is reported. Hydroamination
of terminal and internal alkynes with primary alkylamines, arylamines,
and hydrazines is promoted by 5–10 mol % of Ti catalyst. Various
functional groups are tolerated including esters, protected alcohols,
and imines. The in situ generated complex shows comparable catalytic
activity, demonstrating its synthetic versatility for benchtop application.
Applications of this catalyst for the synthesis of amino alcohols
and a one-pot procedure for indole synthesis are described. A mechanistic
proposal that invokes turnover-limiting protonolysis is presented
to rationalize the observed regioselectivities