Synthesis and resolution of a 1,1′-biazulene analogue of BINOL†

Biaryls exhibiting axial chirality have been extensively exploited in fields such as asymmetric catalysis, but the biaryl linkage typically consists of benzenoid aromatic rings, with non-benzenoid biaryls being scarce. Here we report the first preparation of a (non-benzenoid) 1,1′-biazulene-2,2′-diol (“1,1′-BAzOL”) in enantiopure form and determine its barrier to racemisation. Furthermore we transformed a 1,1′-biazulene-2,2′-diol into the corresponding 2,2′-bis(phosphonate), thereby demonstrating functional group interconversion through cross coupling and highlighting the potential for diversification.