Relation entre structure et réactivité dans les réactions d'addition nucléophile sur les dérivés carbonylés: influence de la tension angulaire sur la réactivité de cyclanones et cyclanols angulairement contraints

Abstract

The rate constants for addition of sodium borohydride on the angularly constrained cyclic ketones, tricyclo[3.3.1.1.3,7]-2-decanone (1), bicyclo[3.3.1]-9-nonanone (2), bicyclo[3.2.1.])-8-octanone (3), and bicyclo[2.2.1.]-7-heptanone (4), have been determined in water/dioxane (50:50 v/v) at 25 °C. These values demonstrate the energy differences caused by the changes in torsion angles on passing from the initial state to the transition state. The activation energies determined, representing almost all of the energy associated with the angular torsion, are indicative of a late transition state.Comparison of rate constants for the reduction of these ketones where the reaction site carbon changes from sp2 to sp3 hybridization with the rates for chromic acid oxidation of the corresponding alcohols (opposite change of hybridization) demonstrates that the effects of the angular variations can also act as criteria for the determination of the position of transition states along the reaction pathway. [Journal Translation]