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

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.

本研究针对十六种携带4位和5位吸电子基团或供电子基团的o-羟基苯乙酮的串联醛醇缩合反应进行了探究，采用无水乙醇中五摩尔当量的SiCl4作为反应介质。携带有吸电子基团（EWGs）（0 < ∑σ > 0.63）的底物在平衡状态下生成了异螺环吡喃（产率12–74%），而携带有供电子基团（EDGs）（∑σ < −0.31）的底物则产生了香豆基盐（产率50–80%）或热致变色双螺环吡喃（产率73%）。这些研究结果对于开发具有可切换光致变色和热致变色特性的新型有机材料具有重要意义。