Cycloaddition

By: William Sommer, Aldrich ChemFiles 2009, 9.5, 7.

Aldrich ChemFiles 2009, 9.5, 7.

Following their work developing chiral gold complexes for the enantioselective hydroamination, Toste and coworkers looked at the [2+2] cycloaddition of allenenes.1 Resulting from this work was the first catalyzed cycloisomerization of allenenes to alkylidenes-cyclobutanes. The cycloaddition reaction yields enantioenriched bicyclo[3.2.0]- structures. In a typical reaction, 3 mol % of gold catalyst is used with 6 mol % of AgBF4 in methylene chloride at room temperature. Good yields and selectivity are obtained for the various bicyclic products (Scheme 1).


Scheme 1.

More recently, the Toste group reported the [4+2] and [4+3] cycloaddition of allene dienes.2 Using a triarylphosphite-gold complex, a series of allene-dienes were reacted. The reaction showed good tolerance for substituents on the diene. Using 5 mol % of the gold catalyst with 5 mol % of AgSbF6 in methylene chloride at room temperature a variety of cycloadducts containing a quaternary carbon were obtained in good yields (Scheme 2). It is important to note that all reactions were diastereoselective affording exclusively the trans-fused cycloadducts in good yields.


Scheme 2.

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Materials

     

References

  1. Luzung, M. R. et al. J. Am. Chem. Soc. 2007, 129, 12402.
  2. Mauleón, P. et al. J. Am. Chem. Soc. 2009, 131, 6348.

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