Helicenes from Diarylmaleimides

Perkin condensations
of arylglyoxylic acids with arylacetic acids,
followed by the addition of alkylamine, yield diarylmaleimides in
a one-pot procedure. The arylglyoxylic acids are obtained by arene
acylation with ClCOCO2Et and reduced with NaI and hypophosphorous
acid to the arylacetic acids. With 2,7-di-tert-butyl-pyren-4-yl
or chrysen-6-yl as the aryl, photocyclodehydrogenation of the diarylmaleimides
yields substituted helicenes which can be reduced to stable anions.
The helicenes combine bathochromically shifted absorption with hypsochromically
shifted fluorescence with respect to their precursors.