The synthetic route employed to access the target compounds
5–8 is outlined in Scheme 1. Alkylation of 2-chlorobenzimidazole
9 was effected with 4-fluorobenzyl bromide 10 under basic conditions
to afford 11 in excellent yield. Attempted palladium-catalysed
Buchwald–Hartwig type amination of 11 under standard
conditions only yielded starting materials, but 12 could be obtained
in good yield after treatment of 11 with excess piperazine
in the absence of catalyst under microwave irradiation. Final coupling
of 12 with 4,7-dichloroquinoline 13 afforded target compound
5.15 Amination of 13 with propanolamine 14 gave
intermediate 15 in excellent yield. Compound 6 was then obtained
by subsequent triflation of 15 to yield 16, followed by nucleophilic
substitution of the triflate with 12.