Abstract Condensation of indolin-2-one (oxindole) lactim ether with malononitrile leads to 2- dicyanomethylidene-2, 3-dihydroindole, the reaction of which with dimethylformamide diethyl acetal (or with triethyl orthoformate) and the subsequent cyclization afford 4- cyanopyrido [4, 3-b] indoles (γ-carbolines). 3-Amino-4-cyanopyrido [4, 3-b] indole was used in the synthesis of substituted pyrimido [4, 5-c]-γ-carbolines.
![1-aminopyrimido-[4,5-c]-γ-carboline Structure](https://image.chemsrc.com/caspic/099/374762-67-1.png)
![N,N-Dimethyl-N'-11H-pyrimido[5',4':5,6]pyrido[4,3-b]indol-1-ylimi doformamide Structure](https://image.chemsrc.com/caspic/491/374760-62-0.png)
