Design, synthesis and conformational analysis of turn inducer cyclopropane scaffolds: microwave assisted amidation of unactivated esters on catalytic solid support to obtain γ-turn mimic scaffolds

Novel constrained 1-aroyl-cyclopropane-2,3-cis-dicarboxylic acid bis-[(2-hydroxy-ethyl)-amides] (17a-e) with varied torsional angles have been synthesized in high yield from unactivated esters of 1-aroyl-2,3-cis-diethoxycarbonylcyclopropanes (15a-e) on a catalytic solid support with reduced reaction times by using the monomode-microwave irradiation; 15a-e were obtained by diastereoselective ethoxycarbonylmethylene transfer from a sulfur ylide to ethyl β-aroylacrylates (10a-e). Torsional angles and interatomic distance measurements on the energy minimized structures of the obtained molecules (17a-e, DFT, B3LYP/6-31G∗ level) have established these molecules as valuable γ-turn mimic scaffolds.