GENERATION AND REACTIONS OF SP(2)-CARBANIONIC CENTERS IN THE VICINITY OF HETEROCYCLIC NITROGEN-ATOMS

This chapter discusses that the generation of a carbanionic center adjacent to a neutral heteroatom, such as nitrogen, is often a difficult proposition and this is a consequence of several factors, of which charge repulsion by the heteroatomic lone pair, low acidity of the hydrogen to be abstracted, and undesired reaction at other reactive sites in the molecule are all major deterents. Repulsion between the lone pair of electrons and the negative charge can significantly reduce the thermodynamic stability of the system. This chapter explores that several different approaches have been explored in a search for possible solutions to these problems, with the majority of these having dealt with the activation of the desired site toward deprotonation and/or the prevention of undesirable side-reactions. Although the degree of success has been quite varied, numerous methods are now available that allow carbanion formation adjacent to nitrogen with predictable ease. © 1993, Academic Press, Inc.