Abstract
A variety of seleno and telluroiminium salts were obtained by reacting the corresponding seleno and telluroamides with methyl triflate at room temperature for 30s. X-ray molecular structure analysis, 13C NMR spectra, and molecular orbital calculations of seleno- and telluroiminium salts suggested that the electrons on the chalcogen atom of the salts are somewhat delocalized with respect to the iminium group, and C-Se and C-Te bonds have a partial double-bond character. Aromatic thio- and selenoiminium salts reacted with a lithium acetylide at their iminium carbon atoms, whereas the aromatic telluroiminium salt reacted at the tellurium atom. This difference in reactivity was elucidated by molecular orbital calculations of the model compounds. Based on the reactivity test of a series of chalcogenoiminium salts, two types of new reactions were developed. Alkynylation of thio- and selenoiminium salts led to α, β-unsaturated ketones. The reaction involves the [1, 3] -shift of MeS- and MeSe-groups to give aminoallenes as intermediates. Alternatively, the sequential reactions with organolithium and -magnesium reagents selectively gave propargylamines. The wide applicability of these reactions is also shown.
