Calixpyrrole derivatives: "multi hydrogen bond" catalysts for gamma-butenolide synthesis

Calix[4]pyrrole (1), calix[2]m-benzo[4]pyrrole (2), 10alpha,20beta- and 10alpha,20alpha- bis(4-nitrophenyl)-calix[4]pyrroles 3 and 4, respectively, were found to exhibit various organocatalytic activities in the diastereoselective vinylogous addition reaction of 2-trimethylsilyloxyfuran (TMSOF, 7) to aldehydes. The gamma-hydroxybutenolide products are obtained in fairly good yields and with moderate diastereoselectivity. The structures of the catalysts, as well as the reaction conditions, strongly influence the efficiency of the reaction.