Highly Stereocontrolled Synthesis of trans-2,6-Disubstituted-5-methyl-3,6-dihydropyrans: Stereoselective Synthesis of the Bicyclic Core of Penostatin B

An efficient, mild, and highly diastereoselective strategy for the synthesis of trans-2,6-disubstituted-5-methyl-3,6-dihydropyran ring systems has been developed starting from δ-hydroxy α-methyl α,β-unsaturated aldehydes and allyltrimethylsilane in the presence of a catalytic amount of ZnBr₂ in a highly diastereoselective manner with excellent yield. The versatility of the above method was also demonstrated for the construction of the bicyclic core present in penostatin B in a concise and highly stereoselective manner.