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.
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.
Ujaque
Gregori
G
Department of Chemistry and Biochemistry University of California, Los Angeles CA 90095-1569 USA.
Lee
Patrick S
PS
Houk
K N
KN
Hentemann
Martin F
MF
Danishefsky
Samuel J
SJ
D000447:Aldehydes / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism; D014992:Xylenes / Q000737:chemistry*
D000447:Aldehydes; D014992:Xylenes