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 (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.