Expanding the scope of Enantioselective FerroPHANE-promoted [3+2] annulations with α,β-unsaturated ketones

The planar chiral 2-phospha [3]ferrocenophane I has been shown to be the first efficient nucleo- philic organocatalyst for the enantiose- lective synthesis of cyclopentenyl- phosphonates, through [3+2] cycliza- tions between diethyl allenylphospho- nate and α,β-unsaturated ketones. The same catalyst has also been applied to the highly enantioselective [3+2] cycli- zations of allenic esters with dibenzyli. deneacetone and analogous bis-enones, leading to functionalised cyclopentenes with either monocyclic or spirocyclic structures (ee 84-95%). It has been shown that the residual enone functions in the resulting cyclopentenes can be involved in subsequent cyclization steps to afford unprecedented C₂-symmetric bis-cyclopentenylketones. In order to provide insight into the behaviour of FerroPHANE I as a chiral catalyst in [3+2] cyclisations, the energetically most favoured isomers of the key phosphine-allene adduct have been calculated by DFT methods. Factors likely to control the chiral induction process are highlighted.