Ring-expansion synthesis and crystal structure of dimethyl 4-ethyl-1,4,5,6,7,8-hexa­hydro­azonino[5,6-b]indole-2,3-di­carboxyl­ate

The title compound, C20H24N2O4, is the product of a ring-expansion reaction from a seven-membered hexa­hydro­azepine to a nine-membered azonine. The azonine ring of the mol­ecule adopts a chair–boat conformation. In the crystal, mol­ecules are linked by bifurcated N—H⋯(O,O) hydrogen bonds, generating [010] zigzag chains. The title compound shows inhibitory activity against acetyl­cholinesterase and butyrylcholinesterase, and might be considered as a candidate for the design of new types of anti-Alzheimer's drugs.