From Quinoxaline, Pyrido[2,3-]pyrazine and Pyrido[3,4-]pyrazine to Pyrazino-Fused Carbazoles and Carbolines.

2,3-Diphenylated quinoxaline, pyrido[2,3-]pyrazine and 8-bromopyrido[3,4-]pyrazine were halogenated in deprotometalation-trapping reactions using mixed 2,2,6,6-tetramethyl piperidino-based lithium-zinc combinations in tetrahydrofuran. The 2,3-diphenylated 5-iodo- quinoxaline, 8-iodopyrido[2,3-]pyrazine and 8-bromo-7-iodopyrido[3,4-]pyrazine thus obtained were subjected to palladium-catalyzed couplings with arylboronic acids or anilines, and possible subsequent cyclizations to afford the corresponding pyrazino[2,3-]carbazole, pyrazino[2',3':5,6] pyrido[4,3-]indole and pyrazino[2',3':4,5]pyrido[2,3-]indole, respectively. 8-Iodopyrido[2,3-] pyrazine was subjected either to a copper-catalyzed C-N bond formation with azoles, or to direct substitution to introduce alkylamino, benzylamino, hydrazine and aryloxy groups at the 8 position. The 8-hydrazino product was converted into aryl hydrazones. Most of the compounds were evaluated for their biological properties (antiproliferative activity in A2058 melanoma cells and disease-relevant kinase inhibition).