The reaction of aminomethylisatins (isatin N-Mannich bases) with hexaethylphosphorous triamide leads to the formation of 1,1'-bis(dialkylaminomethyl)-3,3'-bis(indolin-3-ylidene)-2,2'-diones and 1,1'-bis(1,3-dioxo-1,3-dihydroisoindol-2-ylmethyl)-1H,1'H-[3,3']bisindolylidene-2,2'-dione.