ИСТИНА

The synthesis of compounds in which some cyclic system is peri-fused to the indole core remains an important challenge for the modern organic chemistry. Among the enormous range of natural and synthetic bioactive indoles, such compounds occupy a special place due to their importance for medicinal chemistry and pharmacology. In this work, we present a new approach to the synthesis of various types of polycyclic peri-annulated indoles starting from (3-formylindol-4-yl)-substituted donor-acceptor cyclopropanes. Under the treatment with primary amines in the presence of ytterbium(III) triflate, they produce bridged tetracyclic scaffold containing peri-fused indole and tropane fragments via domino reaction; at the first step the corresponding imine is formed, which then is involved in (3+2)-cross-cycloaddition with cyclopropane fragment. Another type of domino reaction occurred when these cyclopropanes react with hydrazines. The first step is similar, i.e., the formation of the corresponding hydrazones. Unlike imines, they contain a nucleophilic NH group, its nucleophilic attack on cyclopropane leads to the opening of a small ring affording a tricyclic system, containing a diazepine moiety peri-annulated to the indole ring. Reduction of the C=N bond followed by cyclization produced another bridged tetracyclic system containing a peri-annulated indole core.