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Bis(amidate)bis(amido) titanium complex: a regioselective intermolecular alkyne hydroamination catalyst.
Jacky C-H Yim1, Jason A Bexrud, Rashidat O Ayinla
1Department of Chemistry, University of British Columbia , 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.
The Journal of Organic Chemistry
|February 11, 2014
Summary
A novel titanium precatalyst efficiently promotes anti-Markovnikov hydroamination of alkynes with various amines. This versatile catalyst tolerates diverse functional groups, enabling synthesis of amino alcohols and indoles.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Synthetic Organic Chemistry
Background:
- Hydroamination of alkynes is a key transformation for synthesizing nitrogen-containing compounds.
- Development of efficient and selective catalysts for anti-Markovnikov hydroamination remains a challenge.
- Titanium-based catalysts offer potential for novel catalytic applications.
Purpose of the Study:
- To report a novel bis(amidate)bis(amido) titanium precatalyst for alkyne hydroamination.
- To investigate the catalyst's efficiency, selectivity, and functional group tolerance.
- To explore applications in synthesizing valuable organic molecules and develop a mechanistic proposal.
Main Methods:
- Synthesis and characterization of the titanium precatalyst.
- Catalytic hydroamination reactions using terminal and internal alkynes with various amines.
- In situ generation and testing of the catalytic complex.
- Mechanistic studies to elucidate regioselectivity.
Main Results:
- The titanium precatalyst efficiently promotes anti-Markovnikov hydroamination of a range of alkynes with primary alkylamines, arylamines, and hydrazines.
- Catalysis proceeds with 5-10 mol % loading and tolerates diverse functional groups (esters, protected alcohols, imines).
- In situ generated complex exhibits comparable activity, highlighting synthetic versatility for benchtop applications.
- Successful applications include synthesis of amino alcohols and a one-pot indole synthesis.
- Mechanistic proposal involving turnover-limiting protonolysis explains observed regioselectivities.
Conclusions:
- A highly efficient and selective titanium precatalyst for anti-Markovnikov alkyne hydroamination has been developed.
- The catalyst demonstrates broad substrate scope and functional group tolerance, enabling practical synthetic applications.
- The findings provide valuable insights into titanium-catalyzed hydroamination and offer a versatile tool for organic synthesis.
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