Der Sterische Verlauf der nucleophilen Cyclopropanöffnung an den vier im Spiro(methylcyclopropan)‐Ring Diastereoisomeren Lanugonen J (Spirocoleonen)

The Stereochemistry of the Nucleophilie Opening of the Cyclopropane Ring in the four Diastereoisomeric Lanugons J (Spirocoleons) Methanolysis of the spiro(methylcyclopropane) moiety in the four diastereoisomeric lanugons J 3 (13 S , 15 R ), 4 (13 R ,15 R ), 5 (13 S ,15 S ), and 6 (13 R ,15 S ) 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 1 H‐NMR spectra exhibit minute but significant differences in the ABMX 3 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.