Synthesis of Spirocyclic Cyclobutenes through Desulfinative Spirocyclisation of gem-Bis(triflyl)cyclobutenes.

A two-step synthesis of less accessible spiro[cyclobutene-1,9'-fluorene] compounds from biaryl-alkynes and 2-(2-fluoropyridin-1-ium-1-yl)-1,1-bis((trifluoromethyl)sulfonyl)ethan-1-ide, which serves as a potent precursor for outstandingly electrophilic Tf C=CH , has been developed. This synthetic methodology includes selective formation of gem-bis(triflyl)cyclobutenes from biaryl-alkynes and Tf C=CH followed by desulfinative spirocyclisation mediated by 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP). Besides, on the basis of the chameleonic reactivity of sulfone functionality, several derivatisations of triflylated spiro[cyclobutene-1,9'-fluorene] products have been successfully achieved.