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

We probed tandem aldol condensations of sixteen -hydroxyacetophenones, carrying electron-withdrawing and -donating groups at positions 4 and 5, using five molar equivalents of SiCl 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.

An easily accessible isospiropyran switch.

In the presence of SiCl4, three molecules of 5'-bromo-2'-hydroxyacetophenone underwent an unexpected tandem aldol condensation to give a novel isospiropyran switch (69%), with X-ray crystallography confirming its structure. The strong Brønsted acid CH3SO3H turned the colorless isospiropyran into its protonated and open form possessing red color. This process was reversed using the Et3N base, with the acid/base toggling repeatable for at least six times (UV-Vis).

A Hexavalent Basket for Bottom-Up Construction of Functional Soft Materials and Polyvalent Drugs through a "Click" Reaction.

Inspired by polyvalency and its prevalence in nature, we developed an efficient synthetic route for accessing a large variety of multivalent and dual-cavity baskets from inexpensive and abundant starting materials. First, the cycloaddition of vinyl acetate to anthracene was optimized to, upon hydrolysis, give dibenzobarrelene derivative 6, which after five functional group transformations and then cyclotrimerization gave heptiptycene dodecaester 4 in an overall 17 % yield. Following that, compound 4 was converted into D symmetric 1, composed of two fused cavitands each holding three terminal alkynes at the rim for conjugation to functional molecules using the highly efficient CuAAC reaction.