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Wetter is better: The direct arylation of thiazoles on water is quicker, cleaner, and higher‐yielding than arylation in organic solvents. The reaction works under mild conditions for an array of aryl iodides, producing 2,5‐diaryl thiazoles in excellent yields. Importantly, novel bi‐heteroaryl compounds are produced without the requirement for stoichiometric organometallic coupling agents.

In this work, we analyze a series of o-hydroxyaryl aldehydes to discuss the interrelation between the resonance-assisted hydrogen bond (RAHB) formation and the aromaticity of the adjacent aromatic rings. As compared to the nonaromatic reference species (malonaldehyde), the studied compounds can be separated into two groups: first, the set of systems that have a stronger RAHB than that of the reference species, for which there is a Kekulé structure with a localized double CC bond linking substituted carbon atoms; and second, the systems having a weaker RAHB than that of the reference species, for which only pi-electrons coming from a localized Clar pi-sextet can be involved in the RAHB. As to aromaticity, there is a clear reduction of aromaticity in the substituted ipso ring for the former group of systems due to the formation of the RAHB, while for the latter group of species only a slight change of local aromaticity is observed in the substituted ipso ring.

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