Sueki S, Guo Y, Kanai M, Kuninobu Y * The University of Tokyo and CREST Science and
Technology Agency, Tokyo, Japan
Rhenium-Catalyzed Synthesis of 3-Imino-1-isoindolinones by C–H Bond Activation: Application
to the Synthesis of Polyimide Derivatives.
Angew. Chem. Int. Ed 2013;
52: 11879-11883
Key words
C–H activation - rhenium catalysis - intramolecular nucleophilic cyclization - polyimides
Significance
Polyimides find application in aerospace engineering and electronic materials because
of their inherent rigidity, strength, heat-resistance, and electrical non-conductance.
However, their low solubility in organic solvents limits processability. The authors
hypothesized that the solubility could be improved by switching the carbonyl group
into an imino group functionalized with pendant alkyl chains. They confirmed their
hypothesis by developing a mild, atom-economical rhenium-catalyzed transformation
that involves sequential C–H activation, intramolecular nucleophilic cyclization,
and elimination of methanol.
Comment
The key step in the reported methodology is the restoration of the C=N double bond
by elimination of a small molecule (methanol). The efficacy of this tactic is evidenced
by the good yields obtained throughout a diverse substrate scope and on a gram-scale
reaction (80% yield). This is the first example of polyimide derivatives having imino
groups; the polymers obtained are highly soluble in toluene, tetrahydrofuran, dichloromethane,
and chloroform. It will be important to explore the mechanical properties of this
new class of polyimides to determine how they compare to their less soluble, carbonyl-containing
counterparts.
