Synthesis of seven-membered fused sultones by reductive Heck cyclization: an investigation for stereochemistry through DFT study

Abstract

An efficient method for the synthesis of seven-membered fused sultones via Pd(0) catalyzed intramolecular reductive Heck cyclization is reported. The method offers the regio- and stereoselective synthesis of highly functionalized benzopyrido-fused or dibenzo-fused sultone derivatives in 80–95% yield under mild conditions. Chemoselective Sonogashira coupling is utilized for the synthesis of cyclization precursors. The stereochemistry of the exocyclic double bond of sultone derivatives is confirmed from single crystal X-ray diffraction. The stereochemistry of the exocyclic double bond in dibenzo-fused sultones is reverse with reference to that of benzopyrido-fused sultones due to the presence of an interaction between the lone pair of nitrogen in pyridine with the electron deficient Pd(II). This interaction is confirmed through DFT (density functional theory) studies. The mechanistic role of water is established through deuterium exchange reaction.