Organolithium reagents, addition with nitrogen

The reaction of alkyllithium reagents with acyclic and cyclic tosylhydrazones can lead to mixtures of elimination (route A) and addition (route B) products (Scheme 22). The predominant formation of the less-substituted alkene product in the former reaction (Shapiro Reaction) is a result of the strong preference for deprotonation syn to the N-tosyl group. Nucleophilic addition to the carbon-nitrogen tosyl-hydrazone double bond competes effectively wiA a-deprotonation (and alkene formation) if abstraction of the a-hydrogens is slow and excess organolithium reagent is employed. Nucleophilic substitution is consistent with an Su2 addition of alkyllithium followed by electrophilic capture of the resultant carbanion. 

Reaction with (172) and other aldoximes may require oxime activation, which can be achieved with the addition of 1 equiv. of BF3-OEt2." " Yields in the addition of organometallic reagents to substituted aldoximes are modest and are a function of the isomeric composition of the oxime ethers, as the (Z)-oxime isomers are reported to preferentially react with organolithium reagents (entries 1 and 2, Table 13). ° The reaction has been employed for the preparation of 6-aminoalkyl-substituted pencillins (entry 3, Table 13)."° Cyclic oxime ether additions have also been evaluated (entries 4 and 5, Table 13). ° With the lability of the nitrogen-oxygen bond, addition to S-substituted isoxazolines provides a potential avenue for stereospecific synthesis of substituted 3-aminoalcohols (entry 5, Table 13). 

Asymmetric addition of organolithium reagents to prochiral diarylimines 6.44 has been performed by Tomioka, Koga and their coworkers with 2.40 as chiral ligand at -100°C in toluene [636,637,638], In these reactions, the presence of a 4-methoxy group and a 2-substituerrt on the nitrogen-substituted aryl ring increase... 

The mechanism of organolithium addition to naphthyl oxazolines is believed to occur via initial complexation of the alkyllithium reagent to the oxazoline nitrogen atom and the methyl ether to form chelated intermediate 17. Addition of the alkyl group to the arena 7t-system affords azaenolate 18, which undergoes reaction with an electrophile on the opposite face of the alkyl group to provide the observed product 4. The chelating methyl... 

Oxazolidinone-Substituted Carbanions. Oxazolidinone-substituted organostannanes readily undergo transmetalation with alkyllithium reagents to the organolithium derivatives which then can undergo nucleophilic addition reactions. -Substituted oxazolidinones can act in this capacity as both a nitrogen source and source of chirality (eq 60). Although the a-stereoselection... 

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