Syntheses of Tetrahydrofurobenzofurans and Dihydromethanobenzodioxepines from 5-Hydroxy-3-methyl-3H-benzofuran-2-one. Rearrangement and Ring Expansion under Reductive Conditions on Treatment with Hydrides

5-Hydroxy-3-methyl-3H-benzofuran-2-one, 5, easily obtained from pyruvic acid and 1,4-cyclohexanedione, was used as a starting material to prepare (±)-5-hydroxy-3a-methyl-2,3,3a,8a-tetrahydro-furo[2,3-b]benzofuran, 10, and (±)-7-hydroxy-5-methyl-4,5-dihydro-2,5-methano-1,3-benzodioxepine, 14. Reduced reactivity relative to 5-hydroxy-3-methoxycarbonylmethylene-3-methyl-3H-benzofuran-2-one, 6, was preliminarily studied. Meanwhile, a plausible mechanism with regard to the formation of 10 and 14, which included cyclization, rearrangement, and ring expansion of hemiacetal, 15, is proposed. Specific carbamates of phenols, 10 and 14, have shown impressive inhibitory activities against human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) ex vivo.