SummaryPhenylglycine esters react with pyruvic acid to give u-met hylsuccinic amides 9 instead of the expected Schiff bases 8, analogously to p-anisidine but unlike aniline.Aza-allylic carbanions (1) are considered important intermediates in organic synthesis2), their generation however suffers from the general disadvantage that the bases used are rather sophisticated (alkali amides, organolithiums, alkali silylamides), difficult to handle in large scale preparations. Access to anions 1 might be possible using conventional bases (alkoxides) provided that electronwithdrawing groups X and/or Y are placed at the end of the aza-allylic chain (e.g. in 2). Carboxy or carbalkoxy azomethines 3 (Y = COOH or COOAlk) respond to this
N-Substituted 9-fluorenimines 1 are easily prepared from primary amines or aminoesters and 9-fluorenimine: their conjugate carbanions 2 are formed by the action of alkoxides and are reprotonated to 1 or to the tautomeric 9-alkylidenaminofluorenes 3 depending upon substituents.2-Aza-allylic carbanions are frequently used in organic synthesis 111; when asymmetrically substituted they have focused considerable interest as ambident anions in prototropic equilibria [2]. Deprotonation of alkylidenamino-substituted C, H-acids is usually accomplished by rather sophisticated bases [ 11, unaccessible on large scale preparations. To circumvent this difficulty we are presently investigating [3] the potentiality of alkylidenamino-substituted C, H-acids further activated by incorporating one of the ends of the aza-allylic moiety into a frame endowed on its own by high acidity. We report now an easy and expeditious synthesis of 9-fluorenimines 1, a class of C,H-acids in which the fluorenylidene residue plays the role of such an activating group, and for which deprotonation is expected to occur with conventional bases such as alkoxides. In fact, carbanions 2 can be generated under mild conditions: their reaction with the simplest electrophile, the proton, has been investigated, and preliminary results on the tautomerization of 1 into the tautomeric 9-alkylidenamino derivatives 3 upon protonation of 2 are also reported.
The product obtained condensing l‐methyl‐5‐nitroimidazole‐2‐aldehyde with 2‐amino‐4‐trideuteriomethyl‐pyrimidine and showing total deuterium incorporation at one of the olefinic carbons and partial deuterium incorporation para to the amino group, served to assign 13C and 1H resonances in the condensation products 3. The nature of the species undergoing condensation has been inferred from labelling experiments and from 1H and 13C nmr spectra of precursors and products in dimethylsulfoxide and trifluoroacetic acid.
Die Schiffschen Basen (I) , die durch Transaminierung zwischen 9‐Fluorenimin und prim. Aminen bzw. Aminoestern erhalten werden, bilden mit Na‐methanolat in THF oder K‐tert.‐butanolat in DMSO teilweise quantitativ die Anionen (II).
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