Azaallyl enolates

The azaallyl oidates, Le. enolates derived from ketone imines or hydrazones are synthetic equivalents of the ketone endates and thus two examples of azaallyl enolates are included in th section. Lithiated cyclrdiexanonephenylimine (151) crystallizes out of hydrocarbon solution as the dimeric diisopropylamine solvate (152). Significant disorder between the cyclohexyl and the phoiyl moieties is obse ed in this crystal structure however, it is clear that there are no V-az yl carbm contacts in this structure. This lithiated imine structure can be compared with the lithittted dimethylhydrazone of cyclohexanone... 

Closely related to the 1,4-additions of enolates are the reactions of 1- and 2-azaallyl anions. 

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. 

While the abstraction of protons adjacent to the carbon-nitrogen double bond of imines/imine derivatives has been utilized for tiie regioselective generation of azaallyl anions (which are useful in asymmetric ketone synthesis), it competes with and often prevents the addition of nucleophiles to imines. For this reason, imine additions often involve azomethines (e.g. benzylidineanilines) which are not capable of enolization. Many potentially useful additions, however, involve substrates capable of proton abstraction. By avoiding in certain instances some of the structural features of imines/imine derivatives and the reaction conditions responsible for proton abstraction, products resulting from this serious side reaction can be minimized. 

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