δ-Sultone Formation Through Rh-Catalyzed C−H Insertion

Rhodium-catalyzed reactions of sulfonate ester derivatives are biased strongly toward 1,6-insertion and thus offer a general method for assembling δ-sultones. Two protocols for staging this cyclization reaction are described, which capitalize on the unique ability of either diazo or iodonium ylide intermediates to form Rh-carbene species. The value of these heterocycles for fine chemicals synthesis is demonstrated in both reductive and oxidative reactions that make possible excision of the −SO3− moiety.