Ring opening of 2H-pyrans promoted by organometallic reagents. Synthesis of dienic alcohols

Abstract

2H-Pyrans react with organoaluminiums, Grignard reagents, and lithium derivatives to afford, with good yield, conjugated dienols resulting from 1,2-addition processes of the organometallic reagent to the dienones in equilibrium with the 2H-pyrans. Those organometallic reagents act on sterically hindered 2H-pyrans to give dienols and unsaturated ketones (1,4- and 1,6-addition products) as by-products.