N-Heterocyclic carbene-palladium catalysts for bisdiene cyclization-trapping under thermal and microwave conditions

ORGN 458

James M. Takacs, jtakacs1@unl.edu1, Ross N. Andrews, randrew2@bigred.unl.edu2, Suman Layek2, Hector Palencia, hpalencia@bsu.edu3, Somasundaram Venkataraman2, and Libbie S. W. Pelter, pelterl@calumet.purdue.edu4. (1) Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, (2) Department of Chemistry, Univ of Nebraska-Lincoln, Lincoln, NE 68588-0304, (3) Department of Chemistry, Ball State University, Cooper Hall, Muncie, IN 47306-0460, (4) Department of Chemistry and Physics, Purdue University Calumet, Hammond, IN 46323
NHC-Pd catalysts derived in situ from the combination of [(allyl)PdCl/IMes•HCl] or the preformed [(IMes)Pd(allyl)Cl] complex are effective for the palladium-catalyzed cyclization-trapping of bisdienes with oxygen and nitrogen trapping reagents (e.g., phenols and sulfonamides). An optimized catalyst system effects the cyclization-trapping with phenol at the 0.01% catalyst loading level with a TON of 7.6 x 103 and TOF of 280 h-1, values higher than typically found for this and related carbocyclizations. The reaction scales well and a trans-substituted six-membered ring product is obtained in excellent isolated yield (84%) on a 10 mmole scale without further optimization of the catalyst system or reaction conditions. A (IMes)Pd-catalyst appears to be slightly faster than the corresponding (IPr)Pd-catalyst in the bisdiene cyclization-trapping with sulfonamides, and the reaction is somewhat faster and affords higher yield with microwave rather than thermal heating under conditions where the measured reaction temperature is approximately the same.

 

Metal-Mediated Reactions and Syntheses
8:00 AM-12:00 PM, Wednesday, 29 March 2006 Georgia World Congress Center -- C302, Oral

Division of Organic Chemistry

The 231st ACS National Meeting, Atlanta, GA, March 26-30, 2006