Calcium(II)-Catalyzed Intra- and Intermolecular Hydroamidation of Unactivated Alkenes in Hexafluoroisopropanol

A combination of a calcium­(II) triflimide salt and hexafluoroisopropanol (HFIP) was found to be a highly efficient promoter system for the intra- and intermolecular hydroamidation of unactivated alkenes. Unlike other methods, a vast array of functional groups is tolerated at the nitrogen and alkene moieties. The reaction produces the corresponding nitrogen-containing compounds in excellent yields and good diastereoselectivities. The use of HFIP as solvent proved crucial for the proper carrying out of this transformation. Its role, as well as that of calcium and its NTf2 ligand, was rationalized by DFT computations. These calculations show how the [(NTf2)­Ca­(HFIP) n ]+ complex can activate the amide via a basic site of the NTf2 ligand and the alkene with one acidic HFIP proton. The acidity of HFIP is exacerbated by the coordination to the calcium center, the more so as n increases.