Synthetic protocols for the key functionalizations of the photochromic dihydroazulene scaffold

1,8a-Dihydroazulene-1,1-dicarbonitrile (DHA) is a photochromic molecule which upon irradiation undergoes ring-opening to a vinylheptafulvene (VHF). The system has many possible sites for functionalization and hence for tuning of its properties. In this account we summarize different synthetic protocols for attaching substituents at the ring carbon atoms of DHA as well as for replacing the cyano groups at position 1. In particular, positions 2 and 7 are most easily accessed, the latter from DHA by a regioselective bromination-elimination protocol.