Design of new anti-Alzheimer drugs: ring-expansion synthesis and synchrotron X-ray diffraction study of dimethyl 4-ethyl-11-fluoro-1,4,5,6,7,8-hexa­hydro­azonino[5,6-b]indole-2,3-di­carboxyl­ate

The title compound, C(20)H(23)FN(2)O(4), is the product of a ring-expansion reaction from a seven-membered fluorinated hexa­hydro­azepine to a nine-membered azonine. The nine-membered azonine ring of the mol­ecule adopts a chair–boat conformation. The C=C and C—N bond lengths [1.366 (3) and 1.407 (3) Å, respectively] indicate the presence of conjugation within the enamine CH(2)—C=C—N—CH(2) fragment. The substituent planes at the C=C double bond of this fragment are twisted by 16.0 (3)° as a result of steric effects. The amine N(Et) N atom has a trigonal–pyramidal configuration (sum of the bond angles = 346.3°). The inter­planar angle between the two carboxyl­ate substituents is 60.39 (8)°. In the crystal, mol­ecules form zigzag chains along [010] by inter­molecular N—H⋯O hydrogen-bonding inter­actions, which are further packed in stacks toward [100]. The title azonino­indole might be considered as a candidate for the design of new Alzheimer drugs.