Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.The non-hydrogen atoms were refined with anisotropic displacement parameters without any constraints. The H atoms of the 7H-Furo[3,2-g][1]benzopyran-7-one ring system were put at the external bisector of the C—C—C angle at a C—H distance of 0.95 Å and a common isotropic displacement parameter was refined (AFIX 43 of SHELXL97). The H atoms of the CH2 groups were refined with common isotropic displacement parameters for the H atoms of the same group and idealized geometry with approximately tetrahedral angles and C—H distances of 0.99 Å (AFIX 23 of SHELXL97). The H atoms bonded to a C atom of a C=C double bond were put at the external bisector of the C—C—C angle at a C—H distance of 0.95 Å but the individual isotropic displacement parameters are free to refine (AFIX 43 of SHELXL97). The H atom of the tertiary C—H group was refined with an individual isotropic displacement parameter and all X—C—H angles equal at a C—H distance of 1.00 Å (AFIX 13 of SHELXL97). The H atoms of the methyl groups were refined with common isotropic displacement parameters for the H atoms of the same group and idealized geometry with tetrahedral angles, enabling rotation around the X—C bond, and C—H distances of 0.98 Å (AFIX 137 of SHELXL97). The H atom of the OH group was refined with a tetrahedral C—O—H angle, enabling rotation around the C—O bond, O—H distance of 0.84 Å, and with an individual isotropic displacement parameter (AFIX 147 of SHELXL97).