Superacid Promoted Synthesis of 9,9′-Spirobifluorenes and Related Aza- and Diazaspirocycles

A variety of 9,9 '-spirobifluorenes and related azaspirocycles and diazaspirocycles have been prepared in high yields by intramolecular Friedel-Crafts reaction using the Bri nsted superacid, triflic acid (CF3SO3H). Compared to weaker Bri nsted acids, the superacid consistently provides better yields along with reduced reaction times and it eliminates the need for heating. The superacid is particularly effective when dicationic electrophilic intermediates are generated in the conversions, for example with the diazaspirocycle syntheses.

Automated summary

A variety of 9,9'-spirobifluorenes and related azaspirocycles and diazaspirocycles have been synthesized in high yields using the Brinsted superacid triflic acid (CF3SO3H) through intramolecular Friedel-Crafts reaction. The superacid outperforms weaker Brinsted acids, providing better yields, shorter reaction times, and eliminating the need for heating. It is particularly effective in the synthesis of diazaspirocycles, involving the generation of dicationic electrophilic intermediates.