The Stereochemistry of the Nucleophilic Opening of the Cyclopropane Ring in the four Diastereomeric Lanugons J (Spirocoleons)

Article abstract of DOI:10.1002/hlca.19860690227

Methanolysis of the spiro(methylcyclopropane) moiety in the four diastereomeric lanugons J 3(13S,15R), 4(13R,15R), 5(13S,15S), and 6(13R,15S) is shown to proceed stereospecifically with inversion of the configuration at the attacked C-atom (C(15)).The resulting epimeric 2-methoxypropyl-substituted hydroxy-1,4-benzoquinones (royleanones) 7a/8a (monomethoxy derivatives) and 7b/8b (dimethoxy derivatives) could be separated by HPLC using the recently described "Non-Aqueous Cation Exchange System".Respective pairs of 1H-NMR spectra exhibit minute but significant differences in the ABMX3 part of the 2-methoxypropyl group.The final structure assignment is based on a single-crystal X-ray analysis of the dimethoxyroyleanone 7b, whose absolute configuration was established by chiroptical correlation with known abietanoids.Thus, methanolysis of 3 and 4 ((R)-configuration at the reaction centre) yielded the royleanones 7a and 7b with (S)-configuration, whereas analogous treatment of 5 and 6 ((S)-configuration at the reaction centre) led to the corresponding derivatives 8a and 8b both having the (R)-configuration in the 2-methoxypropyl side chain.