Synthesis and reaction of 3-hydroxytetrahydro-4H-pyran-4-one

Abstract

Photosensitized oxygenation of 5,6-dihydro-4-methyl-2H-pyran (1) in methanol followed by reduction gave two kinds of allyl alcohols [(2) and (3)] together with the epoxy-ethers (4) and (5). When the reaction was carried out in solvents other than alcohols it gave (2) and (3) exclusively. Ozonization of 4-methylenepyrans (2) and (13) followed by reduction with zinc powder–acetic acid afforded 3-hydroxytetrahydropyrans (11) and (14). Bromination of (14) gave the dibromide (16), which yielded bromopyran (17) and 3-acetoxy-4H-pyran-4-one (18) on treatment with 1,8-diazabicyclo[5.4.0]undecene. However, the reaction of (16) with silver acetate in acetic acid predominantly afforded (17) in excellent yield. Other allied reactions and mechanisms of these reactions are described.