Chiral η6-Arene-Cr(CO) 3 complexes in organic synthesis: A short and highly selective synthesis of the 18-nor- seco-pseudopterosin aglycone

Abstract

The chiral synthetic building block 5,6-dimethoxy-1-tetralone-Cr(CO) 3 ( 7; >99% e.e.) was converted in only nine steps and with high regio- and diastereocontrol into the 18-nor- seco-pseudopterosin aglycone 3 (50 % overall yield). The synthesis is centrally based on the specific reactivity of the arene-Cr(CO) 3 substructure, especially on the stabilization of negative charge in benzylic position. The trans-configuration of the two benzylic substituents is secured by diastereoselective protonation of an anionic intermediate generated by conjugate addition of 4-methyl-3-pentenyl-lithium to complex 9, prepared from 7 via Peterson olefination, ortho-silylation and benzylic deprotonation/methylation.