A four-component reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, 1,2-dibromoethane, and hydrazines

A four-component reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, 1,2-dibromoethane, and hydrazines under metal-free conditions is described, providing a novel and efficient approach to 2-arylsulfonyl hydrazones. This transformation proceeds smoothly via insertion of sulfur dioxide under mild conditions with good functional group tolerance.