2-Amino-3,4-dicyano-5-mercaptopyrrole

Diamino-3,4-dicyanothiophene is thus converted by NaOH to 2-amino-3,4-dicyano-5-mercaptopyrrole (Scheme 132) (58JA2822). Here, prior to the recyclization of the intermediate (396), a rotation around the 4,5-bond has occurred. With other substrates such as (397), recyclization results in a thiophene, different from the precursor. Here the 3-substituent is involved in the cyclization and so a rotation around the 3,4-bond is mandatory. One can therefore postulate an intermediate of the type (398) in such reactions ring closure of this will lead to a thiophene-3-carbonitrile which could be either (399) or (400). Some examples are shown in Scheme 133 (75JPR861, 77JCR(S)294). 

A mixture of 2-amino-3,4-dicyano-5-mercaptopyrrole and triethyl orthoformate refluxed 6 hrs., the crude intermediate dissolved in ethanol, ethanolic NHg, satd. at 0°, added, and stored 2 days at room temp. 4-amino-5-cyano-6-ethylthio-pyrrolo[2,3-d] pyrimidine. Y 78%. F. e. s. E. G. Taylor and R. W. Hendess, Am. Soc. 87, 1995 (1965). 

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