Tandem oxidative radical brominative addition of activated alkynes and spirocyclization: switchable synthesis of 3-bromocoumarins and 3-bromo spiro-[4,5] trienone

A K₂S₂O₈-mediated tandem radical brominative addition of alkynoates, oxidative spiro-cyclization, and 1,2-migration of esters is reported for the synthesis of 3-bromocoumarins with high efficiency. The prepared 3-bromocoumarins are successfully converted into 3-alkynyl and 3-phosphite coumarins under mild conditions. The synthesis of a specific bromo-incorporated spiro-[4,5]trienyl-2,8-dione is achieved under the same conditions when N-methyl-N,3-diphenylpropiolate is used as the substrate.