L’anion fluorure comme base en synthèse organique: methylénation des cycloalcanediols-1,2 par le dichlorométhane; nouvelle méthode de préparation des diméthylène-2,3 norbornanes

Abstract

1,2-cycloalcanediols heated in CH₂Cl₂/DMF (or DMSO) containing an excess of CsF furnish the corresponding 1,3-dioxolanes when the hydroxyl groups are in a cis-eclipsed conformation. This technique can be applied to sensitive diols (e. g. 5,6-dimethylidene- exo,exo-2,3-norbornanediol) that are not catechols. Double elimination of HCl from 2,3-bis(chloromethyl)-norbornanes occurs in the same conditions, thus uncovering a new method of preparation of 2,3-dimethylidene-norbornanes in mild conditions. Methylenation of 1,2-diols can be carried out by CH2C12/KOH/phase transfer catalyst; in these conditions the elimination of HCl from trans-5,6-bis (chloromethyl)-exo,exo-2,3-norbornane-diol does not occur.