Stereocontrolled Access to Benzo‐Annelated all‐cis‐ and cis,cis,cis,trans‐[5.5.5.6]Fenestranones and all‐cis‐[5.5.5.5]Fenestranes

Abstract

The synthesis of three multiply substituted fenestrindanes (all‐cis‐tetrabenzo[5.5.5.5]fenestranes) is described in detail. Depending on the stereochemical course of the twofold Michael addition of a 1,3‐indanedione to a dibenzylideneacetone in the very first step, the corresponding all‐cis‐tribenzo[5.5.5.6]fenestranones or the strained cis,cis,cis,trans isomers are obtained. In the latter case, stereochemical adjustment to the all‐cis configuration can be achieved by base‐induced epimerization. Conversion of the all‐cis‐[5.5.5.6]fenestranones in five subsequent steps affords the target fenestrindanes bearing either methyl groups at four of the inner (bay) positions or methoxy groups at four or six of the outer (peripheral) positions of the molecular framework.