Enolate ions as beta-activators of ortho-metalation: direct synthesis of 3-aminoindenones
beta-Ketonitriles derived from a Claisen condensation of benzoate esters with alkyl- or phenylacetonitriles lead to 3-aminoindenones in the presence of excess LDA. This new reaction is also applicable to pyridine carboxylic esters. All of the 3-aminoindenones and their aza analogues can be hydrolyzed by acid to give the corresponding 1,3-indandiones. The mechanism of the reaction falls into the directed-ortho-metalation class in which the initial enolate ion of the keto-nitrile directs self-metalation at an ortho position. The new anion then cyclizes onto the nitrile group to generate an aminoindenone. Surprisingly the simplest member of the series, benzoylacetonitrile, does not undergo cyclization. Mechanistic isotope studies revealed that this substance preferentially and directly forms a dianion on the side chain, which is not further deprotonated at the ortho position of the aromatic ring.
Kayaleh
NE
Department of Chemistry, State University of New York at Stony Brook, 11790-3400, USA.
Gupta
RC
Johnson
F