Domino Reaction\nfor the Synthesis of Substituted Pyrano[3′,4′:3,4]cyclopenta[1,2‑<i>c</i>]chromenes Involving Double Ring Formation

Herein, we present a green cascade approach for synthesizing\na\nrange of chemoselective polysubstituted pyrano[3′,4′:3,4]cyclopenta[1,2-<i>c</i>]chromenes containing a chiral stereocenter. The strategy\ninvolves a metal-free nucleophilic reaction between dialkyl (2<i>E</i>)-2-{2-oxo-3-[(2<i>E</i>)-3-aryl-2-propenoyl]-2<i>H</i>-chromen-4-yl}-2-butenedioates and α,α-dicyanoolefins\nunder reflux conditions in ethanol solvent. Mechanistic studies have\nshown that the reaction proceeds via a cascade of steps, including\nMichael addition, intramolecular C- and <i>O</i>-cyclization,\nintramolecular trans-esterification, [1,2]-<i>H</i> and\n[1,5]-methoxy- and ethoxy carbonyl shift, and finally aromatization\nto yield the desired product. In this method, three bonds (2C–C\nand C–O) form in one pot, simultaneously forming two new cyclopentane\nand pyrano rings by double cyclization reactions. Other advantages\nof this method are that it has a simple operation, readily available\nstarting materials, a chemoselective cascade process, transition metal-free,\nsynthetically useful yields, and green conditions by using ethanol\nas a solvent.