Theoretical studies on rhodium(I) catalyzed (5+2) cycloadditions

ORGN 694

Peng Liu, pliu@chem.ucla.edu1, Paul Ha-Yeon Cheong, hycheong@chem.ucla.edu1, Zhi-Xiang Yu, yuzx@pku.edu.cn2, Claude Y. Legault, cyl@chem.ucla.edu1, Paul A. Wender, wenderp@stanford.edu3, and K. N. Houk, houk@chem.ucla.edu1. (1) Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive, East, Los Angeles, CA 90095-1569, (2) College of Chemistry, Peking University, Beijing, 100871, China, (3) Department of Chemistry, Department of Molecular Pharmacology, Stanford University, Stanford, CA 94305
The origins of substituent effects on reactivities and regioselectivities of the Rh(I)-catalyzed (5+2) cycloadditions between vinylcyclopropanes (VCPs) and alkynes were investigated by density functional theory. Heteroatom and bulky alkyl substituents at the 1-position of VCP dramatically increase the rate of this reaction. This difference in reactivity could be attributed to the steric effects, and the stabilization of the allyl intermediates by the conjugation or homoconjugation with the substituents. The regioselectivity with substituted alkynes is controlled by the steric effects of the substituent on the alkyne, moderated by electronic effects. Bulkier group on alkyne tends to be adjacent to rhodium to prevent the repulsion with substituent on VCP. Electron-withdrawing substituent on alkyne decreases this selectivity by stabilizing the transition state in which the substituent on alkyne is distal from rhodium.
 

Materials, Devices and Switches, Metal-Mediated Reactions, Asymmetric Reactions, Total Synthesis, Biologically-Related Molecules and Processes
7:00 PM-9:00 PM, Wednesday, April 9, 2008 Morial Convention Center -- La Louisiane, Blrm. C, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Sci-Mix

Division of Organic Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008