Palladium-catalyzed synthesis of novel tetra- and penta-cyclic biologically active benzopyran- and pyridopyran-containing heterocyclic systems

Abstract

Syntheses of novel tetra- and penta-cyclic benzopyran and pyridopyran derivatives, via direct intramolecular arylation of 2-iodophenoxymethylhetarenes and 3-(2-bromo-pyridin-3-yloxymethyl)-benzo[4,5]imidazo[2,1-b]thiazole in the catalytic system Pd(OAc)2/Xantphos/Cs2CO 3/Ag2CO3 in toluene, and a one-pot bicatalytic method for 12H-[1]benzopyrano[3′,4′:4,5]thiazolo[3,2-a]benzimidazole directly from 3-chloro-methylbenzo[4,5]imidazo[2,1-b]thiazole and 2-iodophenol, are described. This latter compound exhibits high cytotoxicity (MG-22A, 6 μg/mL) on the mouse hepatoma cancer cell line and low toxicity (LD 50, 1058 mg/kg) on the mouse Swiss albino embryo fibroblasts 3T3. © ARKAT-USA, Inc.