Bases Triethylamine-Lithium bromide

When 2,2-dimethylpropanal is used to prepare the azomethine moiety, the corresponding azaallyl anion may be obtained when l,8-diazabicyclo[5.4.0]undec-7-ene/lithium bromide is used as base. The subsequent addition to various enones or methyl ( )-2-butenoate proceeds with anti selectivity, presumably via a chelated enolate. However, no reaction occurs when triethylamine is used as the base, whereas lithium diisopropylamide as the base leads to the formation of a cycloadduct, e.g., dimethyl 5-isopropyl-3-methyl-2,4-pyrrolidinedicarboxylate using methyl ( )-2-butenoate as the enone84 89,384. 

Triethylamine in THF can be used as the external base to deprotonate triazolium salts. The resulting NHCs were complexed in situ, e.g., to [(/7 -cymene)RuCl2]2, [(/ -cod)RhCl]2, and [(/ -C5Me5)RhCl2]2. Sodium carbonate in water/ DMSO deprotonates imidazolium iodides in the presence of mercury(II) dichloride to give [Hg(NHC)2][Hgl3Cl]. " A pyridine-functionalized imidazolium salt was deprotonated by lithium diisopropylamide (LDA) in THF and attached in situ to [(p -cod)Pd(Me)Br] [Eq.(17)]. After abstraction of the bromide anion with silver(I) a tetranuclear ring is formed. 

The S n2 reaction product, p-aminoesters 372, produced from the reaction of allyl bromide 371 and arylamine by treatment with triethylamine, could be converted into substituted p-lactams in the presence of base. Conventional bases such as ethylmagnesium bromide, -butyllithium, potassium tert-butoxide, lithium hydroxide and potassium hydroxide used in such cyclizations failed to give p-lactam 373. However, Sn[N(TMS)2]2 as a base in the cyclization of p-aminoesters could successfully cyclize 372 to give p-lactam 373 (Scheme 4.120). Under optimized cyclization conditions, it was found that 1.5 equiv. of Sn[N(TMS)2]2 in toluene under reflux for 6 h achieved the best yield (up to 83%.)... 

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