Mechanistic insight on the stereoselective photooxidation of enecarbamates using PTAD, a singlet oxygen analog

CHED 439

Catherine Hooper1, Thomas Poon, tpoon@jsd.claremont.edu2, Roberto Franz, rf394@columbia.edu3, J Sivaguru3, Steffen Jockusch3, Nicholas J. Turro, turro@chem.columbia.edu3, and Waldemar Adam4. (1) Claremont McKenna College, Story House, Box 559, 742 N. Amherst Ave, Claremont, CA 91711, (2) Joint Science Department, Claremont McKenna, Pitzer, and Scripps Colleges, W.M. Keck Science Center, 925 N. Mills Ave., Claremont, CA 91711, (3) Department of Chemistry, Columbia University, 3000 Broadway, Havemeyer Hall, New York, NY NY 10027, (4) Department of Chemistry, University of Puerto Rico, Rio Pietras, PR 00931, USA, and Institut für Organische Chemie, Universität Würzburg, D-97074 Germany
Stereoisomeric pairs of chiral enecarbamates 1a-1d can be resolved using singlet molecular oxygen, the smallest known enophile (C&EN, Aug. 23, 2004, p.7). Resolution occurs via the selective reaction of singlet oxygen with one of the diastereomers of the mixture (racemic at C-3') to form a dioxetane, which cleaves upon warming to yield one of the enantiomers of methyldesoxybenzoin in up to 97% enantiomeric excess. The explanation for this remarkable selectivity is currently unknown, but is suspected to involve either the deactivation of singlet oxygen by C-H vibronic coupling via the isopropyl group of the oxazolidinone moiety or a directing effect from the carbonyl oxygen. 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), a highly reactive enophile with similar reactivity to singlet oxygen, has also been found to react stereoselectively with 1a-1d, lending credence to the aforementioned processes. A comparison of the extent of selectivity between PTAD and singlet oxygen will be presented.

 

Undergraduate Research Poster Session: Organic Chemistry
11:15 AM-1:15 PM, Monday, 14 March 2005 Convention Center -- Hall D, Poster

Division of Chemical Education

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