(5S,11aS)-5-Hydro-per-oxy-1,5,11,11a-tetra-hydro-[1]benzothieno[3,2-f]indol-izin-3(2H)-one.

The absolute configuration of the title compound, C14H13NO3S, was assigned from the synthesis and confirmed by the structure determination. The central six-membered ring of the indolizine moiety adopts an envelope conformation, with the greatest deviation from the mean plane of the ring being 0.661 (2) Å for the bridgehead C atom. The benzothiene ring attached to the indolizine ring system is planar to within 0.008 (2) Å. In the crystal, mol-ecules form chains parallel to the b axis via O-H⋯O hydrogen bonds.