Enantio- and regioselective CpRu-catalyzed Carroll rearrangement

The addition of unstabilized carbonyl nucleophiles to allyl-metal fragments still represents a challenge for generating stereo selectively tertiary (and quaternary) stereogenic centers. In this context, the decarboxylative Carroll rearrangement of secondary and tertiary allyl beta-ketoesters is particularly interesting since chiral gamma,delta-unsaturated ketones are obtained. Herein, we show that CpRu half-sandwich complexes can, in the presence of selected enantiopure diimine ligands, catalyze this transformation and afford complete conversions and decent level of enantiomeric excess. Zwitterionic adducts of a hexacoordinated phosphorus anion and CpRu moieties were also associated and shown to generate air-, moisture-, and microwave-stable catalysts that can be readily purified and recycled. Carroll re-arrangements of allylic beta-ketoesters performed with these zwitterionic species occur with better regio- and enantioselectivity.