Lewis acid impact upon stepwise and concerted Diels-Alder reaction mechanisms

CHED 602

Anthony J. Ross, rossa1153@duq.edu1, Joshua A Plumley, plumleyj@duq.edu2, and Jeffrey D. Evanseck, evanseck@duq.edu1. (1) Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, (2) Center for Computational Sciences, Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave, Pittsburgh, PA 15282
After years of debate, the Diels Alder reaction is now well understood. There are two possible mechanisms to follow: concerted or stepwise. Since the 1980's, Prof. Ken Houk has supported the concerted mechanism, where a single transition structure describes the delocalization of six electrons involving the cyclic formation and breaking of σ and π-bonds. On the other hand, the stepwise mechanism, backed by Michael Dewar, is a two step process involving two transition structures and a biradical intermediate. In most cases, the concerted mechanism is energetically favored over the corresponding stepwise mechanism. However, some factors, such as the perturbation caused by Lewis acids can alter the mechanism. Our interest is in determining how Lewis acids affect the reaction energetics and stereochemistry of the Diels-Alder reaction. In this study, the rich and exciting debate leading to a modern day understanding is summarized to provide insight into possible Lewis acid effects.
 

Undergraduate Research Poster Session: Organic Chemistry
11:00 AM-1:00 PM, Monday, March 26, 2007 Hyatt Regency Chicago -- Riverside Center, Poster

Division of Chemical Education

The 233rd ACS National Meeting, Chicago, IL, March 25-29, 2007