The origin of endo stereoselectivity in the hetero-Diels-Alder reactions of aldehydes with ortho-xylylenes: CH-pi,pi-pi,and steric effects on stereoselectivity |
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Authors: | Ujaque Gregori Lee Patrick S Houk K N Hentemann Martin F Danishefsky Samuel J |
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Affiliation: | Department of Chemistry and Biochemistry University of California, Los Angeles CA 90095-1569 USA. |
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Abstract: | Theoretical studies of stereoselectivity have been carried out with B3LYP and MP2 calculations. The high endo selectivity of hetero-Diels-Alder reactions of ortho-xylylenes with acetaldehydes is shown to result from attractive CH-pi interactions between alkyl groups of the aldehyde and the aromatic ring in the transition states of the reaction. For the hetero-Diels-Alder reactions of ortho-xylylenes with benzaldehyde, the stereoselectivity is shown to be mainly governed by the attractive pi-pi interactions between the phenyl rings of the benzaldehyde and the ortho-xylylene. MP2 calculations are necessary to reproduce the stabilizing dispersion interactions. |
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