The reaction of 2-amino-1,4-naphthoquinones with ninhydrin at 50-60°C in acetic acid leads to 4b,11b-dihydroxy-4b,5-dihydrobenzo[f]indeno[1,2-b]indole-6,11,12(11bH)-triones I [R = H, n-Pr, n-Bu, etc.; X = H, 8-OH].The products were isolated as hydrates and when heated in DMSO with methanesulfonic acid, they converted into 13-R-benzo[f]isochromeno[4,3-b]indole-5,7,12(13H)-triones II.