Synthesis of alkylated carbonyl‐bearing furans via acid‐catalyzed Friedel‐Crafts reaction

Abstract Carbonyl‐bearing furans, certain pyrroles, and thiophenes were alkylated using alcohols in an acidic medium. Some 5‐alkylated derivatives of 2‐furoic acid with various adamantyls‐, cycloalkyl‐, other 2°‐ and 3°‐alkyl substituents were synthesized using 2‐furoic acid as a biomass‐derived chemical platform. Side reaction resulted in the substitution of the carboxylic group, leading to the formation of 1,5‐dialkyl furans. In the alkylation of acyl and formyl furan, either mono‐ or di‐alkyl products were obtained, depending on the functional group present in the furan nucleus. Pyrroles (or thiophenes) with related functional groups exclusively (or near‐exclusively) yielded mono‐alkyl products. The resultant 5‐substituted carbonyl furans can be used as building blocks and synthetic equivalents for 1 C and 4 C synthons, as demonstrated by a series of reactions involving 5‐adamantan‐1‐yl‐2‐furoic acid.