The title compound, C15H19NO4, is the a product of the esterification of the corresponding carbonic acid with methanol. The mol­ecule comprises a fused tetra­cyclic system containing three five-membered rings (2-pyrrolidinone, tetra­hydro­furan and di­hydro­furan) and one seven-membered ring (azepane). The five-membered rings have the usual envelope conformations, with the quaternary C atom being the flap atom for the 2-pyrrolidinone ring, and the ether O atom being the common flap atom for the remaining rings. The seven-membered azepane ring adopts a chair conformation with the methine and middle methyl­ene C atoms lying above and below the mean plane defined by the remaining five atoms. The carboxyl­ate substituent is rotated by 77.56 (5)° with respect to the base plane of the tetra­hydro­furan ring. In the crystal, the mol­ecules are bound by weak C—H⋯O hydrogen-bonding inter­actions into puckered layers parallel to (001).

The two epimers from the unusual thermal C6-epimerization of 5-oxo-1,2,3,5,5a,6,7,9b-octa­hydro-7,9a-ep­oxy­pyrrolo­[2,1-a]iso­indole-6-carb­oxy­lic acid, 5a(RS),6(SR),7(RS),9a(SR),9b(SR) and 5a(RS),6(RS),7(RS),9a(SR),9b(SR) have similar geometries but differ in their hydrogen-bonded crystal-packing modes

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