Aromatic biheterocycles

Synthesis, structure, and properties of aromatic biheterocycles 97AHC(67)1. 

Steel, P. J., Aromatic Biheterocycles Syntheses, Structures, and Properties,... 

Several new alternatives to the classical methods of synthesis of biheterocycles have been developed. Most notable among these are low-valent transition metal-catalyzed homo-coupling reactions, which are particularly applicable to the synthesis of biheterocycles, and which give much better yields than the earlier Ullmann and Busch procedures. Furthermore, un-symmetrical biheterocycles are now more readily available by way of palladium-catalyzed cross-coupling reactions, such as the Stille and the Suzuki procedures. Thus, many new members of the biheterocyclic series are now available for study. As a consequence of the increased sophistication of molecular structure determination techniques, aromatic biheterocycles have been the subject of many recent spectroscopic and X-ray crystallographic studies, as well as numerous molecular orbital and molecular mechanics calculations. 

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