The crystal structure of (S)-(-)-6-Bromo-5,7-dihydroxy-8-methyl-2-phenyl-2,3-dihydro-4H-1-benzopyran-4-one [(-)-6-bromocryptostrobin] and a C N.M.R. study of (±)-cryptostrobin and related substances. Revision of the structures of the natural products (±)-lawinal, unonal, 7-O-methylunonal and isounonal

Abstract

The crystal structure of (S)-(-)-6-bromo-5,7-dihydroxy-8-methyl-2-phenyl-2,3-dihydro-4H-1-benzopyran-4-one [(-)-6-bromocryptostrobin] (11) has been determined by X-ray diffraction from diffractometer data at 295 K and refined by block diagonal least squares to a residual of 0.050 (810 'observed' reflections). Crystals of (11) are tetragonal, P4₃2¹2, a 7.849(4), c 46.83(2) Å, Z 8. The crystallographic data are consistent with the S configuration previously proposed for (-)-cryptostrobin (10). The ¹³C n.m.r, spectra of (±)-cryptostrobin and(±)-strobopinin also lead to the structures (1) and (6), respectively. This work has enabled the structures proposed for the natural products (±)-lawinal, unonal, 7-O-methylunonal and isounonal to be revised to (8), (14), (15) and (12), respectively.