Diels−Alder Exo Selectivity in Terminal-Substituted Dienes and Dienophiles: Experimental Discoveries and Computational Explanations

Yu-hong Lam, Paul Ha-Yeon Cheong, José M. Blasco Mata, Steven J. Stanway, Véronique Gouverneur, K. N. Houk
2009 Journal of the American Chemical Society  
The Diels-Alder reactions of a series of silyloxydienes and silylated dienes with acyclic α,βunsaturated ketones and N-acyloxazolidinones have been investigated. The endo/exo stereochemical outcome is strongly influenced by the substitution pattern of the reactants. High exo selectivity was observed when the termini of the diene and the dienophile involved in the shorter forming bond are both substituted, while the normal endo preference was found otherwise. The exo-selective asymmetric
more » ... der reactions using Evans' oxazolidinone chiral auxiliary furnished a high level of π-facial selectivity in the same sense as their well-documented endo-selective counterparts. Computational results of these Diels-Alder reactions were consistent with the experimental endo/ exo selectivity in most cases. A twist-asynchronous model accounts for the geometries and energies of the computed transition structures.
doi:10.1021/ja8079548 pmid:19154113 pmcid:PMC2635921 fatcat:zk6jgifbefabtfve3cnkcdvrw4