Diels-Alder反応におけるπ面選択性と発現機構

概要

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Controlling of the π-facial stereoselectivity in Diels-Alder reactions has been one of the most fundamental and attractive subjects of theoretical and experimental studies.<BR>Increasing attention has been focused on the selectivity in the reaction of 5-substituted cyclopentadienes, the simplest diene having unsymmetrical π-plane. The, π-facial selectivity is highly dependent on the substituents 1) The diene having 5-alkyl or 5-trimethylsilyl group reacted with dienophiles with anti-π-facial selectivity; 2) 5-Hydroxy, 5-acetoxy, or 5-fluoro moiety leads to the opposite stereochemical results. The former case is simply attributable to the steric repulsion between the substituents and dienophiles. However, the origin of the syn selectivity in the latter case has been the subject of intensive studies.<BR>The present paper describes a short review on the theories developed for the prediction and explanation of the π-facial selectivity in the Diels-Alder reactions of these simple dienes.