Three-component synthesis of arylsulfonyl-substituted indolo[2,1- a ]isoquinolinones and benzimidazo-[2,1- a ]isoquinolin-6(5 H )-ones by SO 2 insertion and radical cascade cyclization.

An efficient arylsulfonylation/cyclization of 2-aryl- N -methacryloyl indoles with potassium metabisulfite and aryldiazonium tetrafluoroborates was developed. A series of variously substituted arylsulfonyl indolo[2,1- a ]isoquinolin-6(5 H )-ones were formed in moderate to good yields via utilization of the nature abundant inorganic salt potassium metabisulfite as a SO 2 surrogate. Additionally, this three-component protocol can also be employed for the synthesis of arylsulfonyl-substituted benzimidazo-[2,1- a ]isoquinolin-6(5 H )-ones.