Flipping fast: Head-to-tail cyclic thiazole tetramers representing flexible π-expanded cyclooctatetraenes were designed and synthesized (see picture). The presence of fused thiazole rings in a head-to-tail arrangement leads to a strong columnar stacking of the shallow saddle-shaped π-conjugated molecules, an unusually low inversion barrier of 6.8 kcal mol−1, and reduction-induced complete planarization to an aromatic ring system.
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Mouri et al. (2012) studied this question.