Oxy-and Aminofurans

Many natural products and natural aroma components contain 2-furanone units and considerable synthetic work has thereby been engendered. In the context of these natural products, the name butenolide is generally employed and compounds are therefore numbered as derivatives of 4-hydroxybutenoic acid and not as a furan, for example a tetronic acid is a 3-hydroxybut-2-enolide. 

Butenolides can be converted into furans by partial reduction of the lactone, then dehydration.  

Synthons which have been developed for butenolide construction include 2-trimethylsilyloxyfuran, which reacts with electrophiles at (furan) C-5, and, complimentarily, furans carrying an oxy-tin (or oxy-boron) substituent, which, via chelation control, react with electrophiles at C-3.  

2-t-Butoxyfuran, available from the reaction of 2-lithiofuran with t-butyl perbenzoate, can be lithiated at C-5, reaction with a carbonyl component, then hydrolysis with dehydration, furnishing alkylidene-butenolides.  

2-Trimethylsilylfurans are converted into the butenolide by oxidation with peracid.  

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