Action des composes organomagnesiens sur les pyrones-2—IX : Etude des différentes voies réactionnelles

The formation of the dihydropyranol 15 during the synthesis of the 6-hydroxy-4-heptene-2-one (Z) 14 indicates the possibility of an equilibrium between ketols (Z) 5 and pyranols 6. This equilibrium lies well to the side of the pyranol. It might be argued that the dihydropyranol compounds prepared from 2-pyrones and Grignard reagents can be derived from the Z ethylenic ketols.Criteria for the reaction scheme are provided by the stereoselectivity of intermediates in agreement with MNDO (modified neglect of diatomic overlap) calculations.A brief discussion of the present knowledge on the different reaction schemes concerning the reaction of Grignard reagents with 2-pyrones is added.