Iron-Promoted Sulfinative Cyclization of N-Bromoacetyl Cyanamide with Inorganic Sulfur Dioxide Surrogate via Radical-Polar Crossover Reaction.

An iron-promoted sulfinative cyclization for the preparation of amidine-imbedded sultines under the mild conditions was described, in which available N-bromoacetyl cyanamide and easy-to-handle sodium dithionite, acting as an easy-to-handle sulfur dioxide surrogate and a readily reductant, facilitated the assembly of the target sultines via a radical-polar crossover pathway in a sustainable manner. This protocol is highly amenable to exploring the chemical space relevant to the construction of sulfur heterocycles incorporating nitrogen functionalities.