One-Pot Oxidative Heteroannulations to 5-Aminocoumaran Derivatives

Significance

A one-pot oxidative heteroannulation procedure of N-sulfonylanilines with styrene derivatives to give N-protected coumarans is reported. An extensive optimization study revealed acetonitrile being the best solvent and the phenyl­iodonium ditriflate to be the optimum oxidizing agent. In studies of substrate scope, it was shown that sulfonyl protection is important, as the reaction failed when R^¹ = COPh or COCF₃. Furthermore, hindered substrates give low yields or no reaction (R^³ = 2,6-Me₂). Electron-rich styrenes underwent smooth reaction giving high yields whereas results with more electron-deficient styrenes were not satisfactory. Based on a proposed tentative reaction pathway, a Lewis acid catalyst was tested and Cu(OTf)₂ was found to be the best catalyst for electron-poor substrates. However, ­aliphatic olefins failed in the reaction.