Synthesis of 4- and 4,5-Functionalized Imidazol-2-ylidenes from a Single 4,5-Unsubstituted Imidazol-2-ylidene

Abstract

Using the nucleophilicity of NHCs and aNHCs, as well as the leaving group ability of the former, the carbon-carbon double bond of imidazol-2-ylidenes can be readily mono- and di-functionalized. These results provide also a new light on the formation of abnormal carbene adducts from classical unsaturated NHCs.

Alkali‐Metal‐Mediated Magnesiations of an N‐Heterocyclic Carbene: Normal, Abnormal, and “Paranormal” Reactivity in a Single Tritopic Molecule

“…[14] Both indirect (by Robinsons lithiated NHC and Et 2 Zn) [15] and direct (by Hevias sodium TMP-zincate reagent) [16] methods of zincating IPr at C4 have also been reported. An unusual amido-directed lateral lithiation of aC H(Me) 2 wingtip on aD ipp (diisopropylphenyl) group in a4 -amido NHC has recently been described by Braunstein and co-workers.…”

Serendipitous reactions involving a silicone grease

“…Addition of a small amount of silicone grease directly to THF significantly increased the yield of 29. [28], which contains an abnormal carbene unit previously demonstrated by Bertrand [29]. It is noted that the reaction mixture including 31 was so reactive that activation of Si O bonds in silicone grease occurred to provide trinuclear iron complex 32, which was crystallized in the presence of a cryptand (Chart 10).…”

Coordination chemistry of ditopic carbanionic N-heterocyclic carbenes

“…8) [46]. Addition of potassium bis(trimethylsilyl)amide led to the deprotonation of the imidazolium cation to generate an "abnormal" carbene as an intermediate (15), however intramolecular rearrangement of 15 yielded the C4-functionalized NHC 16.…”

“…Generation of C4-functionalized NHCs (16) via the formation of mesoionic carbene intermediates(15) [46].…”