Synthesis of Highly Substituted Cyclobutanes <i>via</i> Silver‐Catalyzed Reaction of Pyrazole and Propargyl Carbonates

Abstract A regio‐ and stereoselective Ag(I)‐catalyzed synthesis of fully substituted cyclobutane derivatives from 3°‐propargyl carbonates and pyrazole was developed. The intermolecular tail‐to‐tail [2 + 2] cycloaddition products were obtained in good yields, involving the cleavage of the C─O bond and the formation of C─N and C─C bonds.The halo groups are tolerated under the reaction condition. Sterically encumbered 9‐fluorenyl containing cyclobutane has been synthesied. The switching of product formation from dimethylenecyclobutane to 3,3‐diphenyl‐allyl‐gem‐dipyrazole (DP‐ADPs) was observed when the reactions were performed with other Lewis acids and Brønsted acid. Radical scavenger experiments were performed to explore the reaction mechanism. The scale‐up reaction also proceeded well without comprimizing the yield of the four‐membered compound. The crystal structure of bromo‐substituted four‐membered compound reveals weak intermolecular C─H···N and C─H···C interactions. The photophysical properties of the final compounds have been studied in solution phase and solid‐state. Notably, the cyclobutane derivatives exhibited strong solid‐state fluorescence emissions.