Bromine-Promoted One-Pot Furo[ b ]annulation and α-C(sp 2 )-Thiomethylation Cascade of ( E )-3-Styrylquinoxalin-2(1 H )-ones with Dimethyl Sulfoxide.

A new process has been developed for the bromine-promoted sequential (sp ² )C = (sp ² )C bond functionalization of ( E )-3-styrylquinoxalin-2(1 H )-ones and furo[ b ]annulation via the 5- exo- cyclization in dimethyl sulfoxide (DMSO). The reaction represents a novel strategy for the synthesis of 2-aryl-3-(methylthio)furo[2,3- b ]quinoxalines and involves 3-(1,2-dibromo-2-arylethyl)quinoxalin-2(1 H )-ones and 2-arylfuro[2,3- b ]quinoxalines as key intermediates. Furthermore, DMSO was converted to dimethyl sulfide in situ, which served as the methylthiolation reagent in the reaction. This protocol constitutes an efficient and convenient method for the annulation and methylthiolation of ( E )-3-styrylquinoxalin-2(1 H )-ones bearing a wide range of functional groups in high yields at room temperature.