Divergent Synthesis of Helical Ketone Enabled by Rearrangement of Spiro Carbocation

An acid-mediated electrophilic cyclization of 2-alkynyl-1,1 '- biphenyls for the divergent synthesis of angular, bent, and zigzag fused nonplanar conjugated organic molecules was realized. The key feature of this reaction is a Wagner-Meerwein-type rearrangement via a spiro carbocation intermediate, which was formed by electrophilic cyclization of the 9H-fluoren-9-one derivative at the meta position. The products can be advanced to helical fluorenes, which exhibit high fluorescence quantum yields.

Automated summary

An acid-mediated electrophilic cyclization of 2-alkynyl-1,1'-biphenyls was used to synthesize angular, bent, and zigzag fused nonplanar conjugated organic molecules. The reaction involved a Wagner-Meerwein-type rearrangement via a spiro carbocation intermediate formed by electrophilic cyclization of a 9H-fluoren-9-one derivative. The resulting products could be further transformed into helical fluorenes with high fluorescence quantum yields.