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One-Pot Aldol Cascade for the Preparation of Isospiropyrans, Flavylium Salts, and bis-Spiropyrans

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posted on 11.06.2020, 12:39 by Taylor A. Neal, Allyson B. Eippert, Austin Chivington, Andrew Jamison, P. Chukwunalu Chukwuma, Curtis E. Moore, Jennifer F. Neal, Heather C. Allen, Laura M. Wysocki, Noel M. Paul, Jovica D. Badjić
We probed tandem aldol condensations of sixteen o-hydroxyacetophenones, carrying electron-withdrawing and -donating groups at positions 4 and 5, using five molar equivalents of SiCl4 in anhydrous ethanol. Substrates carrying electron-withdrawing groups (EWGs) (0 < ∑σ > 0.63) populated the equilibria with isospiropyrans (12–74% yield), while those carrying electron-donating groups (EDGs) (∑σ < −0.31) gave flavylium salts (50–80%) or thermochromic bis-spiropyrans (73%). The results are of interest for developing novel organic materials possessing switchable photochromic and thermochromic characteristics.