Syntheses of β‐Lactones, 6. One‐Step Synthesis of β‐Lactones by Aldolization of Ketones or Aldehydes with 1‐Acylbenzotriazoles

Benzotriazolides 1 of alkanoic acids with one hydrogen atom in α‐position to the carboxamide group can be deprotonated with lithium diisopropylamide or lithium hexamethyldisilazanide to amide enolates 2 which condense at −90 to −95°C with ketones or aldehydes 3 to afford benzotriazolides of O‐lithiated β‐hydroxylalkanoic acids 4. These reactive carboxamide derivatives cyclize with elimination of lithium benzotriazolide to the corresponding di‐ and trisubstituted β‐lactones. With regard to the formation of β‐monosubstituted β‐lactones from aldehydes the use of benzotriazolides as active carboxylic acid derivatives proved to be superior to the application of the corresponding phenyl esters. An α‐unsubstituted β‐lactone 6 was obtained from 1‐acetylbenzotriazole only with cyclohexanone. The other carbonyl compounds 3 did not provide the corresponding α‐unsubstituted β‐lactones 6.