Carbanions nitrogen stabilization

However, in a nitrogen ylide R3 —C 2 (see p. 39), where a positive nitrogen is adjacent to the negatively charged carbon, only the field effect operates. Ylides are more stable than the corresponding simple carbanions. Carbanions are stabilized by a field effect if there is any hetero atom (O, N, or S) connected to the carbanionic carbon, provided that the hetero atom bears a positive charge in at least one important canonical form,90 e g.,... 

Dipole-Stabilization is a term coined by Beak to describe the situation that results when a carbanion is stabilized by an adjacent dipole. Such a situation arises when, for example, an amide is deprotonated a to nitrogen. The chemistry of these systems has been reviewed, - so only a few pertinent points will be made here. Firstly, metalation occurs syn to the carbonyl oxygen, and when the system is cyclic, the equatorial proton is removed selectively, and the electrophile attacks equatorially, as shown in equation (5), 24, 25 Thus, in contrast to nitrosamines, amide anions give the less stable equatorial product. 4,i25... 

Enantioselective deprotonations a to the oxygen or nitrogen atoms of carbamates 4.1 and 4.2 can be performed with s-BuLi in the presence of sparteine 2.5. The pro (5)-hydrogen atom is selectively removed, and lithiated carbanions 4.3 are formed. These carbanions are stabilized by dipolar interactions [982] and coordination to sparteine [564, 983-987], Such species are stable up to -30°C, and react with electrophiles at -78°C with retention of configuration [984-987]-... 

Oxazolium salts (11) are known to react with stabilized carbanions, nitrogen, oxygen, sulfur, and halogen at both the C-2 and C-5 positions. Reaction at the C-2 site results in the formation of... 

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