Activation and Substitution of 1-Ferrocenylalkylamines with Allenones: Application to Three-Component Synthesis of 4-(1-Ferrocenylalkyl)pyrazoles

A one-pot, two-step three-component synthesis of 4-(1-ferrocenylalkyl)pyrazoles has been developed involving activation and substitution of 1-ferrocenylalkylamines with allenones under mild conditions. A range of 1-ferrocenylalkylamines reacted with allenones in the presence of dipicolinic acid at room temperature without extrusion of air and moisture, and the resulting crude products were treated with hydrazine to afford structurally diverse 4-(1-ferrocenylalkyl)pyrazoles in moderate to good yields. Moreover, the three-component reaction was successfully extended to an enantioenriched alpha-ferrocenylbenzylamine with complete retention of configuration.