| Abstract: | A novel Lewis acid‐catalyzed [3+4] annulation of 2‐(heteroaryl)cyclopropane‐1,1‐dicarboxylates with cyclopentadiene is reported. This reaction proceeds via an electrophilic attack of the Lewis acid‐activated donor‐acceptor cyclopropane onto cyclopentadiene followed by Friedel–Crafts intramolecular alkylation of the heteroarene substituent. This is the first general example of reactions of donor‐acceptor cyclopropanes wherein the donor substituent serves as a nucleophile. The described annulation represents a convenient approach to bicyclo[3.2.1]octa‐2,6‐dienes with heteroarenes annulated to C(2)‐C(3) bond. Its efficiency was demonstrated for a series of furyl, thienyl, pyrrolyl, benzofuryl, benzothienyl, and indolyl substituted cyclopropanes. Additionally, in the case of 2‐(5‐methyl‐2‐furyl)cyclopropane‐1,1‐diester we observed the predominant formation of product of the [3+4] annulation or the tetracyclic 5,8‐methanocyclopenta[a]azulene derivative, depending on the reaction conditions. |
