Power of P: Phosphine‐promoted [3+2] annulation reactions between electron‐poor allenes and 3‐arylidene indolin‐2‐ones afford a new organocatalytic strategy for the synthesis of the spirocyclic core of oxindolic cyclopentanes (see scheme). Asymmetric variants of these reactions have been implemented by using chiral catalysts, giving very high levels of asymmetric induction.

The planar chiral 2-phospha[3]ferrocenophane I has been shown to be the first efficient nucleophilic organocatalyst for the enantioselective synthesis of cyclopentenylphosphonates, through [3+2] cyclizations between diethyl allenylphosphonate and alpha,beta-unsaturated ketones. The same catalyst has also been applied to the highly enantioselective [3+2] cyclizations of allenic esters with dibenzylideneacetone 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 C(2)-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.

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A new family of planar chiral phosphoramidites with a [3]ferrocenophane structure was synthesized. The synthetic strategy involved diastereoselective formation of the chiral ferrocene units from suitable substituted biscyclopentadienyl derivatives. Preliminary coordination studies of these ligands were undertaken with the synthesis of palladium and platinum complexes. Article pubs.acs.org/Organometallics