Synthesis of functional allyl-α-tetrahydropyrones from cyrene

Addition of allylzinc to cyrene affords diastereomeric 4-allyl-6,8-dioxabicyclo[3.2.1]octan-4-ols. Opening of their 1,6-anhydro bridge with Ac₂O followed by selective deacetylation of the resulting tertiary and acetal acetates yields diastereomeric 2-acetoxymethyl-5-allyl-tetrahydro- pyran-5,6-diols whose oxidation by the action of DMSO–Ac₂O system is accompanied by etherification of tertiary hydroxy groups leading to methylthiomethoxy pyrone derivatives. The opening of 1,6-anhydro bridge in 4-allyl-6,8-dioxabicyclo[3.2.1]octan-4-ols with MeOH–HCl followed by oxidation with PCC gives individual (4S,6S)- 1-allyl-6-methoxy-2,5-dioxabicyclo[2.2.2]octan-3-one.