Stereoconvergent Direct Ring Expansion of Cyclopropyl Ketones to Cyclopentanones

Recyclization of the ring-opening species of alkyl cyclopropyl ketones to cyclopentanones, which proceeds through an unfavored 5-endo-trig cyclization predicted by Baldwin's rules, is elusive. Herein, as assisted by a strong aryl donor and the Thorpe- Ingold strain on a quaternary cyclopropyl center, stereoconvergent direct ring expansion of cyclopropyl ketones to cyclopentanones promoted by TfOH or BF3 center dot Et2O is described, providing a modular construction of polysubstituted cyclopentanones from aldehydes, alkyl methyl ketones, and alpha-keto esters within three steps.

Automated summary

Assisted by a strong aryl donor and the Thorpe-Ingold strain on a quaternary cyclopropyl center, stereoconvergent direct ring expansion of cyclopropyl ketones to cyclopentanones promoted by TfOH or BF3•Et2O is described, providing a modular construction of polysubstituted cyclopentanones from aldehydes, alkyl methyl ketones, and alpha-keto esters within three steps.