Generation of chirality in 4,4′-azopyridine by co-crystallization with optically active dicarboxylic acids

The co-crystals of anti-4,4′-azopyridine apy with optically active 9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid 1 and trans-1,2-cyclohexanedicarboxylic acid 2 were prepared and their solid state CD spectra were measured. The positive Cotton effect sign, corresponding to the lowest energy n–π∗ transition, was correlated with the M helicity of the twisted Ar–NN chromophore. The absolute sense of the twist of the guest apy molecule was deduced from the X-ray structures of the (S,S)-1·apy and (S,S)-2·apy complexes.

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(11S,12S)-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acidC18H14O4Ee >97%[α]D22=-9.2 (c 4, MeOH)Source of chirality: resolutionAbsolute configuration: (11S,12S)