Synthesis of cyclopropane derivatives via an efficient stereoselective trimerization procedure

Cyclopropanes are valuable intermediates that can be used in a wide array of biochemical process and in medicinal chemistry owing to a unique combination of reactivity and structural properties [1,2]. In this work, quaternary ammonium salts (4) is prepared by the reaction of phenacyl bromides (2) with the 1,4-Diazabicyclo[2.2.2]octane (3). Deprotonation with potassium carbonate as a mild base forms the corresponding ylide, which undergoes trimerization reaction to give (2,3-bis-(aroyl)cyclopropyl)aryl methanone derivatives (5a-5i) efficiently in a stereoselective manner (Scheme 1). The reaction mixture was purified by using column chromatography to afford the desired pure product. The structures of the products were identified by spectral data. The cis configurations of the products were confirmed by the coupling constant of the vicinal protons of cyclopropane ring [3].