K. Peters et al., Crystal structure of (3aR*,6aR*,9aR*,9bS*)-spiro[(1 ',3 '-dioxolane)-2 ',6-decahydro-9a-methoxycarbonyl-9-oxoazuleno[4,5-c]furan-1(3H)-one], C2H4O2[C12H13O3]COOCH3, Z KRIST-NEW, 214(1), 1999, pp. 103-104
C16H20O7, monoclinic, P12(1)/c1 (No. 14), a = 9.597(1) Angstrom, b = 12.564
(1) Angstrom, c = 13.077(1) Angstrom, beta = 101.22 degrees, V = 1546.7 Ang
strom(3), Z = 4, R-gt(F) = 0.053, R-w(F) = 0.057, T = 293 K.