Synthesis of Heterocycles Using 2-Azadienes

Reports on the synthesis of five-membered heterocycles by intramolecular nitrogen—nitrogen bond formation (N1—N5) came some years ago from our laboratory [79CC891 81 JCS(Pl) 1891 83JCS(P1)2273]. Thus, 4-alkyl(aryl)amino-l-azabutadienes 2, which are readily available in large scale from alkyl(aryl)imines 1 and aliphatic or aromatic nitriles (70S 142  

On the other hand, intramolecular carbon—nitrogen bond formation leading to N-substituted-3-acylpyrroles 5 smoothly occurs in 79-96% yield by heating a solution of azadiene 2 having a propargyl appendage at the enamine carbon atom (R3 = CH2—-C C—R5) in toluene or ethanol/ 

200-240°C (70-82% yield) methanolysis of the latter resulted in the formation of 3,4-disubstituted-5-trimethylsilyl-l-pyrrolines 9 as the sole stereoisomer (68-93% yield). 

The formation of substituted quinolines 35 (58-90% yield) by intramolecular cyclization of 4-arylamino-l-azabutadienes 2 has been carried out at 100°C using one equivalent of aluminium chloride the reaction involves the diene moiety and one carbon—carbon double bond of the aromatic ring (87S82). The participation of the phenyl group attached to the a- 

Similarly, Uneyama and Watanabe (91TL1459) have reported the synthesis of trifluoromethylated AI-aryl-1-azabutadienes by palladium-catalyzed coupling of trifluoroacetimidoyl iodides with alkenes as well as the transformation of the azadiene derived from methyl acrylate into the corresponding 4-methoxycarbonyl-2-trifluoromethylquinoline in quantitative yield. 

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