Ring-rearrangement metathesis of 3,6-dialkoxy-3,6-dihydro-2H-pyrans

The first RCM–ROM–RCM sequence using a non-strained heterocycle as relay moiety is described. The course of the reaction strongly depends on the nature and relative configuration of the substituents in the starting trienic system. In addition, for a productive reaction to be observed, the site of initiation of the metathesis cascade is crucial. The compounds thus obtained may be useful for the synthesis of unusual polydeoxydisaccharides.