Formation of quaternary centres via iron allyl cations. Rapid entry into spirocyclic ring systems

Ester-substituted allyltetracarbonyliron cations react with cycloalkylidene-type silyl enol ethers, silyl ketene acetals, and β-keto-esters to give 1,6-dicarbonyl compounds containing a newly formed quaternary centre. Selected condensation products are converted by enolate chemistry into spirocyclic [4.4], [4.5], and [4.6] systems. Acyloin and other reductive cyclization reactions are employed to convert the condensation products into spirocyclic [4.5], [5.5], and [5.6] systems. Keywords: allyliron complexes, umpolung synthesis, 1,6-dicarbonyls, spirocycle synthesis.