Acid zeolites as catalysts in organic reactions. Friedel-Crafts reaction of 2-alkylfurans with 3-substituted allylic alcohols

Methyl 3-(2-furyl) propanoate (1) and 3-(2-furyl) propyl acetate (3) can be conveniently alkylated with high conversion and selectivity by cinnamyl and crotyl alcohols in the liquid phase at moderate temperatures using acid zeolites of medium and large pore size as heterogeneous catalysts. ZSM-5 zeolite exhibited the highest turnover number for the heteroaromatic alkylation. This reaction was found to be totally regioselective at the 5 position of the substituted heterocyclic ring, as well as chemoselective with regard to either the CC double bond of the allylic alcohol or ester groups on the lateral chain of the furan. However, two alkylation products (linear and branched), arising from a non-regioselective attack on the 1 or 3 position of the allylic alkylating reagent, are generally observed. Formation of the corresponding symmetric ethers by dehydration of the alcohols, especially at lower reaction temperatures and higher alcohol molar ratios, is a competing side reaction.