Construction of sulfonated spiro[5,5]trienones from sulfur dioxide via iron-catalyzed dearomative spirocyclization of biaryls

An iron-catalyzed dearomative spirocyclization of biaryl ynones with sodium metabisulfite and cycloketone oxime esters is developed. By using sodium metabisulfite as the source of sulfur dioxide, this approach enables the rapid assembly of sulfonated spiro[5,5]trienones with broad substrate scope and good functional group tolerance. Mechanistic studies demonstrate the generation of cyanoalkyl and cyanoalkylsulfonyl radicals during the reaction process. This radical-induced transformation proceeds via a 6-exo-trig dearomative spirocyclization process with the insertion of sulfur dioxide.