An application of the PIFA-mediated [PIFA: phenyliodine(III) bis(trifluoroacetate)] biaryl coupling reaction is presented and extended to the formation of heterobiaryl connections. A preliminary study of the scope and limitations of this procedure was carried out in the synthesis of phenanthroids 11 from a series of phenethyl-substituted heterocycles 10. It was observed that in some cases a competitive dimerization process took place. It was also found that the coupling step could be efficiently extended to a larger number of examples if an aromatic ring were situated fused to the 1,2-diarylethane skeleton, as in 23 and 30. The synthesis of a series of 4,5-diarylthiazoles 23a−g was therefore carried out to explore the electronic requirements and the regioselectivity of the PIFA-mediated non-phenolic coupling reaction. When the same procedure was applied to aryl-heteroarylthiazoles 30, a series of phenanthroid-fused thiazoles 31 was obtained in good overall yields. To the best of our knowledge, no oxidative aryl-heteroaryl coupling reaction of this type had previously been reported. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
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Moreno et al. (2002) studied this question.