Stabilised enamine anions. Generation and alkylation of anions stabilised as cyclopentadienide enamine systems

Abstract

Pyrrolidine enamines from indan-1-one, indan-2-one, and 3,4-diphenylcyclopent-2-enone were converted into the corresponding anions (3), (14), and (23) by treatment with n-butyl-lithium in tetrahydrofuran at –65 to 25 °C. Treatment of the anion (3) with methyl iodide provided a methylated enamine which was (a) hydrolysed to 3-methylindan-1-one (82%), (b) subjected to a second anionic methylation to give 3,3-dimethylindan-1-one (95%), and (c) acylated to give 2-benzoyl-3-methylindan-1-one (19%). Corresponding treatment of the anion (14) produced (a) 1-methylindan-2-one (68%), (b) a mixture of dimethylated products (84%), and (c) 3-benzoyl-1-methyl-2-(pyrrolidin-1-yl)indene (51%). Corresponding treatment of the anion (23) gave (a)2-methyl-3,4-diphenylcyclopent-2-enone (51%) and (b) 5-acetyl-2-methyl-3,4-diphenylcyclopent-2-enoene (15%).