An economical and effective protocol for large scale synthesis of the 2-phenyl-1,8adihydroazulene-1,1-dicarbonitrile (DHA) photoswitch has been developed.This compound is ring-opened by light to a vinylheptafulvene (VHF), which is thermally closed back to DHA.This compound serves as an important starting material for dihydroazulene photoswitches incorporating a substituent in the seven-membered ring and as a reference compound for comparison of properties.A detailed NMR spectroscopic characterization has allowed the assignment of all proton and carbon signals.In addition, the compound was characterized by Xray crystallography.A correlation between the rate constant for thermal ring-closure of VHF to DHA and empirical parameters of solvent polarity (ET30) was established.
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Broman et al. (2011) studied this question.
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