Ring-Opening of 1,3-Imidazole Based Mesoionic Carbenes (iMICs) and Ring-Closing Clicks: Facile Access to iMIC-Compounds

Herein, ring-opening of mesoionic carbenes (iMICs) (iMIC=[ArC{N(Dipp)}2C(SiMe3)C:) (Dipp=2,6-iPr2C6H3, Ar=Ph, 4-Me2NC6H4 or 4-PhC6H4) based on an 1,3-imidazole scaffold to yield N-ethynylformimidamide (eFIM) derivatives as crystalline solids (eFIM={(Dipp)N=C(Ar)N(Dipp)}C equivalent to CSiMe3) is reported. eFIMs are thermally stable under inert gas atmosphere and show moderate air stability (t1/2=3 h for Ar=Ph). eFIMs are excellent surrogates of iMICs, which generally have a limited shelf-life, and readily undergo ring-closing click reactions with a variety of main-group as well as transition metal Lewis acids to form hitherto challenging iMIC-compounds in good to excellent yields. In addition to the relevance of eFIMs in the synthesis of iMIC-compounds, quantification of the stereoelectronic properties of a representative iMIC (Ar=Ph) by experimental and theoretical methods suggests remarkably sigma-donor property and steric profile of these new ligand sets. Stable unmasked iMICs are extremely scarce and have limited shelf-life. An unprecedented ring-opening of iMICs to N-ethynylformimidamides (eFIMs) has been reported. eFIMs are thermally stable under an inert atmosphere and show moderately air-stability. They are excellent iMIC-surrogates and readily undergo ring-closing-clicks with a variety of (non)metal Lewis acids, affording iMIC-compounds (iMIC)[M] with zero waste and easy workup.image