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Abstract
Dianions of active hydrogen compounds having two negative charges capable of interacting (by resonance for example) with the same carbonyl or other activating group are of particular interest to organic chemists, since the anionic portion arising through the secondary ionization is much more nucleophilic than that from the primary ionization. Consequently, alkylation can be effected at the secondary site to the practical exclusion of the alkylation at the primary site. For example, the 1,4-dianion of acetophenone oxime undergoes C-alkylation with alkyl halides in 60-80% yield.
Since diazotic acids can be considered to be derived from the oximes by substitution of nitrogen for the methine group, it was thought possible to form dianions of aliphatic diazotic acids by procedures similar to those used with oximes. This was the initial objective of this research.
The potassium diazotates of phenylmethane-, 1-phenylethane-, and octane-1-diazotic acids were prepared in good yields by cleavage of the corresponding N-nitrosocarbamates with potassium t-butoxide. However, attempts to abstract the (alpha)-hydrogen from these diazotates with n-butyllithium were unsuccessful. Therefore, the lithium diazotates were prepared by the treatment of the N-nitrosocarbamates with lithium t-butoxide, a procedure that gave lower yields of the diazotates than treatment with t-butyl lithium but provided more tractable products.
CAUTION! Dried lithium diazotates must be used immediately and handled in the hood behind a safety shield.
When lithium phenylmethanediazotate in ether-HMPA solution was treated successively with n-butyllithium and methyl iodide at -80(DEGREES), three products were isolated: benzylidene n-butylmethylhydrazine, acetophenone n-butylmethylhydrazone, and acetophenone dimethylhydrazone. When lithium octane-1-diazotate was treated in the same fashion, the only identifiable product obtained was n-octylidene n-butylmethylhydrazine. The formation of these unexpected products can be explained by reasonable extrapolations of known chemistry of diazoalkanes and/or nitrosoamines.
