Crystal structure of 3-(3,4,5-tri­meth­oxy­phen­yl)-1,2,3,4-tetra­hydro­cyclo­penta[b]indole-2-carb­oxy­lic acid

In the title compound, C(21)H(21)NO(5), obtained from a Morita–Baylis–Hillman adduct, the hydrogenated five-membered ring adopts a shallow envelope conformation, with the C atom bearing the carb­oxy­lic acid substituent deviating by 0.237 (1) Å from the mean plane of the other four atoms (r.m.s. deviation = 0.007 Å). The dihedral angle between the fused ring system (all atoms; r.m.s. deviation = 0.057 Å) and the pendant trimeth­oxy benzene ring is 66.65 (3)°. The C atoms of the meta-meth­oxy groups lie close to the plane of the benzene ring [deviations = 0.052 (1) and −0.083 (1) Å], whereas the C atom of the para-meth­oxy group is significantly displaced [deviation = −1.289 (1) Å]. In the crystal, carb­oxy­lic acid inversion dimers generate R (2) (2)(8) loops. The dimers are connected by N—H⋯O hydrogen bonds, forming [011] chains. A C—H⋯O inter­action is also observed.