Abstract
A novel and efficient Claisen-type condensation reaction for the synthesis of α,α-disubstituted
β-keto carbonyl compounds from ketones and unactivated carboxylic acids in a P2O5/Tf2O system is presented. This approach can be applied to reactions between various open-chain
ketones, cyclopentanones, indenones, and tetrahydronaphthones and unactivated alkyl
carboxylic acids, aromatic carboxylic acids, and unsaturated carboxylic acids, affording
all-carbon spirocyclic 1,3-diketones of various sizes and acyclic 1,3-diketones containing
all-carbon quaternary centers in moderate to high yields. Furthermore, we have also
confirmed that the reaction proceeds via an enol lactone intermediate.
Key words
Claisen-type condensation - α,α-disubstituted β-keto carbonyl compounds - ketones
- carboxylic acids - P
2O
5/Tf
2O