C5 Metalation of Imidazole-Based Monothiolates en Route to Selenothiolates

Lithiation
of an imidazole-based monothiolate, 2,
by excess n-butyllithium gives a white powder containing
both a lithiated product and an nBuLi contaminant (in a ca. 1:1 molar
ratio). This white powder not only reacts with TMEDA in toluene to
give 4, a C5-lithiated-imidazole-based monothiolate dimer
but also cleaves THF to give a pair of enantiomers of 5 (as a result of “capturing” the LiOCHCH2 fragment by a C5-lithiated-imidazole-based monothiolate monomer).
Further reaction of the lithiated product of 2 with selenium
results in the first dimeric (7) and monomeric (8) selenothiolates. The nature of the bonding in 7 and 8 was further probed by DFT computations.