Crystal structure and absolute configuration of bromoisotenulin

Abstract

Bromoisotenulin crystallises in the monoclinic space group P2₁, a= 8·732(3), b= 23·094(6), c= 10·237(5)Å, β= 121·27(10)°, Z= 4, with two independent molecules in the asymmetric unit. Two sets of data were collected: photographic, 2300 reflections, and diffractometer, 1700 reflections. The structure was solved by Patterson and heavy-atom methods, and the diffractometer data refined by full-matrix least-squares to R 0·075. The results confirm the structure (IV) suggested by Herz et al. and supply the unknown stereochemistry and absolute configuration. The carbon skeleton is biogenetically abnormal, a methyl group having migrated from C(4) to C(5). Both five-membered rings are trans-fused to the seven-membered ring. Attention is drawn to an error in the published stereochemistry of the related compound, bromomexicanin E.