Synthesis of 5-hydroxy-1,7-dioxaspiro[5.5]undec-3-en-2-ones from 2-benzenesulfonyltetrahydropyrans and 5-hydroxybutenolides: X-ray crystal structure determination for (5RS,6SR)-5-acetoxy-4-methoxy3-methyl-1,7-dioxaspiro[5.5]undec-3-en-2-one

Abstract

5-Hydroxy-1,7-dioxaspiro[5.5]undec-3-en-2-ones are obtained from reactions between 2-lithiated 2-benzenesulfonyltetrahydropyrans and 5-hydroxybutenolides. The structure of (5RS,6SR)-5-acetoxy-4methoxy-3-methyl-1,7-dioxaspiro[5.5]undec-3-en-2-one 16 was confirmed by X-ray crystallography. Addition of 5-lithiated 2,3-dihydrofuran and 6-lithiated 3,4-dihydro-2H-pyran to the hydroxybutenolide 12 gave the butenolides 30 and 31. Hydrolysis of 31 gave 33, which on dehydration returned 31 rather the conjugated isomer 32.