After looking at several different approaches to the synthesis, a convergent approach, shown in the Scheme 4, was developed
for large scale synthesis. Bromination of benzazepinone
10 with pyridinium hydrobromide perbromide in chloroform followed by recrystallization gave bromide 11.
Reaction of bromide 11 with ethaneimidate hydrochloride in
the presence of potassium carbonate in toluene or chloroform
gave the desired imidazole 12 in 69% yield. Although chlo-roform provided a slightly better yield, for large scale preparation,
toluene was used to minimize halogenated solvent
waste and because the quality of product was similar or better
than with use of chloroform. Deprotection of the tosylate
was found to be effective with heating the sulfonamide 12 in
80% sulfuric acid at 80oC. The benzazepinone product 13
was obtained in 90% yield after crystallization from acetonitrile
and water mixture.
Synthesis of the coupling partner 16 required to provide
conivaptan was synthesized in 95% yield from biphenyl 2-
benzoic acid via sequential reaction with thionyl
chloride in toluene followed by coupling with aminobenzoic
acid in acetone with N,N-dimethylaniline as a base. High
quality acid 16 was obtained by crystallization from DMF
and water. The acid 16 was activated by converting it into
acid chloride with thionyl chloride in acenonitrile, to which
was added imidazo benzazepine 13 in toluene and, after recrystallization
in acidic ethanol, gave conivaptan hydrochloride
(III) in 90% yield.