The crystal structure of the title compound was determined by X-ray diffraction by use of the multi-solution programs, MULTAN. Crystals are monoclinic, space group P21 with Z= 2 in a unit cell of dimensions: a= 12·956, b= 7·901, c= 9·438 Å, β= 106·10°. The structure was refined by full-matrix least-squares methods to a final R of 0·052 for 1666 observed diffractometer reflections. The seven-membered ring approximates to a twist-chair conformation.