New Way to Substitute Tetracyanocyclopropanes: One-Pot Cascade Assembling of Carbonyls and Malononitrile by the Only Bromine Direct Action

The new type of the chemical cascade reaction was found: formation of cyclopropanes from carbonyl compounds and CH acid by the only bromine direct action. The action of aqueous bromine on the carbonyl compounds and malononitrile in EtOH-H2O solutions in the presence of NaOAc results in the formation of 3-substituted 1,1,2,2-tetracyanocyclopropanes in 48–93% yields. The latter are well-known precursors for the different bicyclic heterosystems, among them those containing cyclopropane ring and those possessing different types of pharmacological activity. 1. Introduction The cyclopropyl group is a vital structural unit in many synthetic and naturally occurring compounds, exhibiting a wide spectrum of biologic properties ranging from enzyme inhibition to herbicidal, antibiotic, antitumor, and antiviral activities [1–5]. Thus, the prevalence of cyclopropane containing compounds with biological activity, whether isolated from natural sources or rationally designed pharmaceutical agents, has inspired chemists to find novel and diverse approaches to their synthesis. Though the methods of cyclopropanes synthesis have long been documented, so far, all of them consist of two main groups: (1) intramolecular cyclization or (2) interaction of two different molecules (addition of carbenes to olefins or Michael initiated ring closure (MIRC) are the most known examples of this type) [1, 3, 5]. Nevertheless there are some special famous methods of the cyclopropane ring construction. One of them is well-known Wideqvist reaction, namely, the interaction of two molecules of bromomalononitrile with carbonyl compounds 1 in the presence of stoichiometric quantity of potassium iodide with the formation of the corresponding substituted tetracyanocyclopropanes 2 (Figure 1) [6]. Figure 1: Wideqvist’s condensation route to tetracyanocyclopropanes. Later in the electrochemical variant of Wideqvist reaction bromomalononitrile was replaced by malononitrile and catalytic amounts of sodium bromide [7, 8]. In the electrochemical variant for the reaction of aldehydes the low temperature 0°C is necessary [8], whereas for ketones a three- to fourfold excess of ketone is needed to obtain tetracyanocyclopropanes 2 in good yields [7, 8]. Recently we suggested a new strategy of the chemical route to the cyclopropane structure: the direct transformation of carbonyl compounds and malononitrile into 1,1,2,2-tetracyanocyclopropanes 2 [9]. Elemental bromine was used as active halogen compound, 1.2 equivalents of EtONa as base, and ethanol as solvent [9]. The next step of our research was direct