Alkoxy-, Hydroxy-, and Aminofurans

The results of recent work justify a summary. The interest centers on the tautomeric structure of these five-membered rings on the one hand, and on a new group of substances on the other. 

2-Alkoxyfurans are best prepared from 2,5-dialkoxy-2,5-dihydro-furans, by acid-catalyzed alcohol eliminations40,242,243  

Nucleophilic substitution of 5-halo-2-furoic acid by methoxide, followed by decarboxylation, gave varying yields351  

2-Alkoxyfurans are unstable compounds. Monomethoxyfuran polymerizes in air. They react with active dienophiles e.g., with maleic anhydride the expected substituted tetrahydro-3,6-epoxy-phthalic anhydride was obtained, which can be aromatized exceptionally easily. 

It is somewhat surprising that these furans are not particularly good dienophiles. However, this is not so in the case of 3-methoxyfurans, which are substantially more active dienes than furan. 

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