On the Solvent-Dependent Bromination of Dihydroazulenes

Abstract Bromination of 1,8a-dihydroazulene-1,1-dicarbonitriles (DHA) followed by elimination of HBr was previously shown to be an important protocol for functionalizing these molecular photoswitches in the seven-membered ring (at C7). Here we show systematically how the outcome of the bromination reaction depends on the electronic character of an aryl substituent at the C2 position of DHA, and the solvent polarity as the reaction can lead to either the addition product or to the corresponding 2-aryl-1-bromo-3-cyanoazulene.