Ca(II)-Mediated Regioselective One-pot Sequential Annulation of Acyclic compounds to Polycyclic Fluorenopyrans

Abstract

Herein we report a facile synthesis of tetracyclic fluorenopyrans from simple acyclic reactants, propargyl alcohols and 3-methylpentane-2,4-dione under calcium catalysis. This one-pot, 3-component reaction proceeds through a sequential allene formation, Friedel-Crafts cyclization/cycloisomerization, intramolecular aldol reaction, Claisen rearrangement, and 6-endo dig cyclization to result in the formation of fluorenopyrans (indeno[2,1-g]chromenes). This strategy was further used in the synthesis of 3-iodo-fluorenopyrans, by adding iodocyclization to the above sequence of reactions (4-CR). Noticeably, this highly practical, atom and the step-economic procedure is catalyzed by a sustainable (alkaline earth) metal salt and tolerates the broad substrate scope, allowing the further transformations and synthetic utilities of these complex polycyclic moieties. (Figure presented.).