Structure and reactivity of some enamines of 1-phenylindan-2-one

Abstract

Enamines of 1-phenylindan-2-one are shown to exist as mixtures of 1-phenyl and 3-phenyl isomers. The isomeric ratio varies with the nature of the amine group, and the factors controlling the ratio are briefly discussed.

The isomeric mixtures are resistant to C-alkylation with electophilic reagents in contrast to the ready alkylation of the pyrrolidine enamine of 3-phenylindan-1-one. The lack of reactivity of the enamines of 1-phenylindan-2-one is ascribed to steric hindrance of nitrogen lone pair–,π-bond overlap, and to stabilising delocalisation of the charge-separated form. Both these factors are absent in the case of 3-phenylindan-1-one enamines.