Calixpyrrole Derivatives: “Multi Hydrogen Bond” Catalysts for γ-Butenolide Synthesis

Abstract

Calix[4]pyrrole (1), calix[2]m-benzo[4]pyrrole (2), 10α,20β- and 10α,20α- 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 γ-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.

Isotopic Labeling Study of the Formation of Calix[5]pyrroles Catalyzed by Bi(NO3)3

“…Recently, we described the first synthesis of 2 by a direct condensation of pyrrole with acetone [7]. This surprising approach was stumbled upon by chance during an exploration of optimal conditions for the synthesis of calix [4]pyrroles using Lewis acids, particularly Bi(NO 3 ) 3 [13]. By decreasing the concentration of the Lewis acid, the yield of 2 was found to increase with respect to the yield of 1, to a maximum ratio of 3:1.…”

“…The most widely studied are the calix [4]pyrroles, largely due to their ease of synthesis [5]. During the condensation of ketones with pyrrole, expanded calixpyrroles are also formed [6].…”

“…A later approach described the synthesis of a calix [5]pyrrole by the reaction of 3,4-difluoropyrrole with acetone, leading to decafluorocalix [5]pyrrole 6 (35% yield), which was stable under the reaction conditions [11]. The authors argued that 6 was difficult to obtain because the parent octafluorocalix [4]pyrrole 5 was the thermodynamic (stable) product and 6 was the kinetic (unstable) product. In 2002, Kohnke et al reported the first synthesis (an indirect synthesis) of a β-unsubstituted calix [5]pyrrole 2 from a calix [5] furan in a 1% yield [9].…”

“…Although the structural features of these compounds are best known for their ability to specifically recognize anions, appropriately functionalized calixpyrroles can recognize ionic pairs by binding to both the anion and the counter cation [2]. [4]pyrroles and calix [5]pyrroles.…”

“…Hydrogen bond-donating catalysts are used in a variety of synthetic transformations, including hetero-Diels-Alder, regioselective alkylation and acylation reactions, as well as vinylogous addition reactions of 2-trimethylsilyloxyfuran to aldehydes to afford γ-hydroxybutenolide products [4].…”