[3+2] Dipolar cycloadditions promoted by a tungsten pi-base

ORGN 109

Kimberley C Bassett, kcb6j@virginia.edu, Fei You, fy8n@virginia.edu, Peter M. Graham, pmgrah@yahoo.com, Michal Sabat, ms5c@virginia.edu, and W Dean Harman. Department of Chemistry, University of Virginia, McCormick Rd, P.O. Box 400-319, Charlottesville, VA 22904
When coordinated to a pi base, such as {TpW(NO)PMe3}, where Tp =hydridotris(pyrazolyl)borate, the carbonyl ylide isomer of the furan complex is accessible and is very reactive towards dipolar cycloaddition with a number of dipolarophiles. The bound carbonyl ylide reacts significantly faster than the free organic. The TpW(NO)(PMe 3)( h2-2,5-dimethylfuran) complex, undergoes a [3+2] dipolar cycloaddition with N -phenylmaleimide to give the 7-oxanorbornene complex with >95:1 selectivity for the exo isomer as indicated by 1H NMR. X-ray crystallography has confirmed the exo isomer. Reactions with acrylonitrile led to the isolation of a mixture of isomers favoring the exo isomer in a 3:1. In both cases, the reaction conditions are mild and neutral, and proceed with >70% yield. Decomplexation of the cycloadduct afforded the free organic compounds in 87% and 76% yields, respectively.
 

Heterocycles, Aromatics, Materials, Devices, Switches, Combinatorial Chemistry, Metal-Mediated Reactions
8:00 PM-10:00 PM, Sunday, 13 March 2005 Convention Center -- Hall D, Poster

Division of Organic Chemistry

The 229th ACS National Meeting, in San Diego, CA, March 13-17, 2005