With Carbon Disulfide for Pyrimidine-2,4-dithiones

An ingenious solution to the problem of slowly reacting (weakly basic) o-aminonitriles was to replace the carbon disulfide by potassium O-ethyl dithiocarbonate ( xanthogenate ) (EtO—CS2K),188 which slowly liberates carbon disulfide above 110°C. Thus, 2-amino-5-nitrobenzonitrile gave an excellent yield of 6-nitroquinazoline-2,4-dithione when boiled with this salt in butanol for 4 hr.189 Excellent yields of 8-azapurine-2,6-dithione and its 9-methyl and 9-benzyl derivatives were similarly obtained.179 For more reluctant reactions, boiling dimethylformamide proved to be a useful solvent.189 

Excellent yields of annelated 4-thioxopyrimidin-2-ones have been obtained by condensing oaminonitriles with carbonyl sulfide (24 hr in boiling etha-nolic sodium ethoxide). Thus, 2-amino-3-cyanothiophene (see 11) gave 4-thioxothieno[2,3-d]pyrimidin-2-one (135), and 3-amino-4-cyanopyrazole (see 15) formed 4-thioxopyrazolo[3,4-rf]pyrimidin-6-one (see 16). The reaction is thought to follow the course of the above carbon disulfide reaction.190 

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