Crystal Structure of the Dimeric (4-tert-ButyhhiazoIato)(glynie)lithium: Carbene Character of a Formyl Anion Equivalent

摘要

The question whether nudeophilic acylalions with reagents of type 1 are possible has a long history. Although compounds of type 1 b are comparatively easily accessible, the species 1 arc only of limited use in synthesis. Not without reason was the concept of "Umpoiung" created in the search for new methods of nudeophilic acylations. One of the problems is that the compounds 1 react like the isorneric alkoxycarbenes V. Some dimerize rapidly even at — 120 °C. This is in agreement with results of quantum-mechanical calculations for lithiated formaldehyde LiCH=O, which predict a C—O bridged structure l"a (R = H, M = Li) with a distinct carbene character. Lithiated aldimines 2 seem to have a smaller propensity for dimerization, but this alternative has not gained any broader application.