Preparation and some reactions of substituted thieno[3,4-b]furans
Treatment of a variety of 3-hydroxythiophenes with either an excess of methyl or ethyl bromoacetate and anhydrous potassium carbonate in acetonitrile under reflux, or in DMSO at room temperature, gave the 3-alkoxy derivatives in good to excellent yields. Utilization of the Dieckmann condensation, using either sodium alkoxide–alcohol or sodium hydride–benzene as base, afforded substituted thieno[3,4-b]furans in moderate to good yields. These compounds were found to exist predominantly in either the keto or enol form dependant upon the nature of substitution in the thiophene ring. Derivatives prepared from thieno[3,4-b]furan compounds showed that the system exhibited the chemical properties associated with ketones, enols, and β-keto esters. In addition the allyl ether was formed from 3-hydroxy-2,4-bismethoxycarbonylthieno[3,4-b]furan which underwent the Claisen rearrangement upon distillation.