Ene and yne dienophiles and substituents: Theoretical insights into surprising substituent effects

ORGN 494

Gavin O. Jones, gjones@chem.ucla.edu1, Mingji Dai, md2204@columbia.edu2, Sun-Joon Min, sjm2130@columbia.edu2, Patrick L. Theofanis, ptheofan@caltech.edu3, K. N. Houk, houk@chem.ucla.edu1, and Samuel J. Danishefsky, s-danishefsky@ski.mskcc.org4. (1) Department of Chemistry and Biochemistry, University of California Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095-1569, (2) Department of Chemistry, Columbia University, Havemeyer Hall, 3000 Broadway, New York, NY 10027, (3) Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Boulevard, Mail Code164-30, Pasadena, CA 91125, (4) Laboratory for Bioorganic Chemistry, Sloan-Kettering Institute for Cancer Research, 1275 York Ave. (Box 106), New York, N.Y. 10021 and, Department of Chemistry, Columbia University, Havemeyer Hall, 3000 Broadway, New York, NY 10027
Substituent effects in Diels-Alder cycloadditions of 1,3-butadiene and 1,3-dimethoxybutadiene (a model for Danishefsky and Rawal dienes) with ester-substituted alkenes and alkynes were studied with B3LYP density functional theory. These studies show that in cycloadditions involving butadiene, the rate of the reaction increases as the number of ester substituents increases in the dienophile (the Alder rule), and that alkynes are as reactive as alkenes. Cycloadditions involving 1,3-dimethoxybutadiene also follow the Alder rule with the notable exception that 1,2-disubstitution with esters significantly reduces the barrier for alkyne cycloadditions, but has only a small effect on alkene cycloadditions. Consequently, alkyne reactivities are greater than those of alkenes in cycloadditions involving very nucleophilic dienes. B3LYP reveals the structural features of the transition state that contribute to these trends. Ethynyl and vinyl substituent effects are also reported.
 

Physical Organic Chemistry, Metal-Mediated Reactions, Asymmetric Reactions and Syntheses
8:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Organic Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007