Pd/Sn Mediated Multicomponent Synthesis of Tetrahydropyrans

Significance

A Pd-catalyzed bimetallic strategy for a three-component cascade coupling to give diaryl-substituted tetrahydropyrans is reported. The sequence begins with a Pd(0)/SnX₂ mediated anhydrous generation of homoallyloxytin (IV) intermediate in a Barbier fashion from the reaction of allyl bromide or allyl chloride with aliphatic or aromatic aldehydes. The formed tin species undergoes cascade coupling in the presence of either an aldehyde or an aryl epoxide to give the tetra­hydropyran products with all cis stereochemistry. Although the mechanism was not established, the coupling between homoallyloxytin(IV) and the aldehyde is assumed to follow a Prins-like mechanism. Yields of products appear not to be dependent on R¹ and R² substitution; however, an insufficient number of cases were tested.