Catalytic hydrogenation of 2-bromo-4-nitrotoluene (I) over Raney-Ni provided aniline (II). Reaction of (II) with chloral hydrate and hydroxylamine gave rise to the isonitrosoacetanilide (III), which was subsequently cyclized to the isatin (IV) by heating in concentrated H2SO4. Oxidative cleavage of isatin (IV) produced the anthranilic acid (V). This was converted to the benzoxazinone (VI) upon refluxing with acetic anhydride. Ring opening of benzoxazinone (VI) with MeOH, followed by acidic hydrolysis of the acetamide function, yielded the anthranilate ester (VII). The quinazoline derivative (VIII) was then obtained by treatment of anthranilate (VII) with chloroformamidine hydrochloride in refluxing diglyme. Finally, displacement of the bromide group of (VIII) with the sodium thiolate of 4-mercaptopyridine (IX) under Ullmann conditions afforded the title pyridyl sulfide.
3-Bromo-4-methylaniline (I) was converted to the isonitrosoacetanilide (II) upon treatment with chloral hydrate and hydroxylamine. Cyclization of (II) in hot sulfuric acid produced the isatin (III) along with its 6-bromo regioisomer. Anthranilic acid (IV) was then obtained by oxidative cleavage of isatin (III). Esterification of anthranilic acid (IV) was achieved by conversion to the benzoxazinone (V) with acetic anhydride, followed by conversion to methyl anthranilate (VI) in boiling methanol. Alternatively, anthranilic acid (IV) was activated as the isatoic anhydride (VII) with triphosgene and then reacted with MeOH. Anthranilate (VI) was converted to the aminoquinazolinone (IX) upon condensation with chloroformamidine hydrochloride (VIII) at elevated temperature. Coupling of bromide (IX) with methyl 4-mercaptobenzoate (X) under Ullmann reaction conditions furnished thioether (XI). The methyl ester group was then hydrolyzed to the acid (XII) with NaOH in aqueous EtOH.