Transition metal complexes in organic synthesis. Part 47.1 Organic synthesis via tricarbonyl(η4-diene)iron complexes

Abstract

The protection of conjugated dienes by coordination to the tricarbonyliron fragment offers many potential applications of the resulting complexes to organic synthesis. The preparation of tricarbonyl(η4-1,3-diene)iron complexes is readily achieved by a 1-azabutadiene-catalyzed complexation of the free ligands. An asymmetric catalytic complexation of prochiral cyclohexa-1,3-dienes with pentacarbonyl-iron using chiral 1-azabutadienes affords chiral nonracemic complexes. The chiral tricarbonyliron complexes of acyclic butadienes represent versatile starting materials for the synthesis of a broad range of polyunsaturated natural products. Consecutive carbon–carbon and carbon–nitrogen bond formations of the tricarbonyliron–cyclohexa-1,3-diene complexes and arylamines provide many biologically active carbazole alkaloids and a tetracyclic subunit of the discorhabdin alkaloids. The iron-mediated [2+2+1] cycloaddition of trimethylsilylacetylenes and carbon monoxide affords stable 2,5-bis(trimethylsilyl)-substituted cyclopentadienones which are useful substrates for further cycloadditions.