3- Cyano-2-methylpyrroles

Aminofurans substituted with electron-withdrawing groups e.g. NO2) are known and 3-amino-2-methylfuran is a relatively stable amine which can be acylated and diazotized. 2-Amino-3-acetylfurans are converted into 3-cyano-2-methylpyrroles on treatment with aqueous ammonia. This transformation is a further illustration of the relative instability of the amino derivatives of five-membered ring heterocycles compared with anilines (Scheme 67) (781003821). 

The amino compounds form salts and acylamino derivatives which are considerably more stable. Interesting ring-opening reactions can be initiated by proton loss from the amino group. Thus, 2-amino-3-ethoxycarbonylthiophenes (383) with ethanolic sodium ethoxide give cyanothiolenones (384) (75JPR86). In a similar sequence 2 amino-3-acetylfurans (385) are converted into 3-cyano-2-methylpyrroles (386) by aqueous ammonia (78JOC3821). 

The principal products of irradiation of 2-cyano-l-methylpyrrole (166) in methanol, however, are the corresponding 3-cyanopyrrole 167 and the methanol adduct 168.129 These products appear to arise by a 2,5-bonding process followed by a thermal walk rearrangement as shown in Scheme 5. 

Although evidence for thermally induced migrations points to a sigmatropic shift of the substituent, as discussed above, the photochemical conversion of 2-cyanopyrrole into 3-cyanopyrrole proceeds by a [1,3] sigmatropic walk of the heteroannular atom by route (a), as shown in Scheme 2. 2-Cyano-3-methylpyrrole and 2-cyano-4-methylpyrrole undergo similar phototranspositions to produce 3-cyano-4-methylpyrrole (by route a) and 4-cyano-2-methylpyrrole (by route a), respectively (75CC786), whilst 2-cyano-5-methylpyrrole produces... 

The formation of pyrroles by the photolysis of furan or thiophene in the presence of a primary amine was considered to involve valence-bond isomers of pyrroles but the latter were not isolated. However, the photoreaction of cyanopyrrole was examined at the same time as that of cyanofuran (Section I,A), and much earlier than that of cyanothiophenes (Section I,B). Irradiation of 2-cyano- 1-methylpyrrole in methanol was reported to give l-cyano-3-methoxy-5-methyl-5-azabicyclo[2.1.0]pentane, which may have been formed from the Dewar compound (Eq. 14).4 The structure of the... 

The cyano group also plays an important role in the photoreaction of 2-cyano-l-methylpyrrole. Hiraoka reported that the photolysis in methanol yields a methanol adduct of a Dewar isomer (113)114). 

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