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DOI: 10.1055/s-2008-1042686
Asymmetric Lithiation of 2-Alkynyl Aryl Sulfides
Contributor(s):Hisashi Yamamoto, Matthew B. BoxerWestfälische Wilhelms-Universität Münster, Germany and Nagoya Institute of Technology, Japan
Asymmetric Lithiation of 2-Alkynyl Aryl Sulfides-Enantio- and Diastereoselective Formation of Allenyl Aryl Sulfides and Their Application in Nickel-Catalyzed Cross-Coupling Reactions
Tetrahedron Lett. 2007, 48: 8636-8642
Publication History
Publication Date:
21 February 2008 (online)
Key words
lithiation - allenyl sulfides - nickel
Significance
The Toru and Hoppe groups have collaborated to publish this interesting paper on asymmetric lithiation of 2-pyridinyl propargyl sulfides and their subsequent addition to aldehydes or protonation. These reactions proceed with good to moderate stereoselectivity. The alkynyl starting material is basically limited to the substrate indicated. The allenyl products were also shown to proceed in a Ni-catalyzed cross-coupling reaction. The stereochemical inversion associated with the lithium-to-titanium transmetallation is quite interesting.
Comment
This is an interesting report in that the absolute stereochemistry in the products is reversed when using hexane compared to either toluene or diethylether. When using hexane as the solvent, the authors note that selective crystallization of the lithiated intermediate occurs. Subsequent transmetallation with titanium and addition to aldehydes is the only method to obtain high selectivity. Using toluene or ether as the solvent results in substrates being solvated the entire time, but lower and reversed selectivities are observed.