DOI:  10.1016/j.tet.2014.09.018

A theoretical and experimental study of the racemization process of hexaaza[5]helicenes

A dynamic ¹H NMR study, together with DFT calculations, of bis-([1,2,3]triazolo)[1,5-a:5′,1′-k][1,10]phenanthroline 2 has allowed to identify the ring and open forms of a new example of ring/chain tautomerism, as well as their interconversion barriers (ring/ring and ring/open). The barrier of the exchange process between the chain forms and the ring form was found higher than the ‘racemization’ process in the closed form, so the ring opening does not contribute to the ‘racemization’. The di-1,10-methyl and di-1,10-iodo derivatives have been prepared and their properties calculated.shifts, ¹H–¹H coupling constants and electronic spectra reduced the 20 possible structures to only one, the 3,3′-Z,Z-anti-azopyrazole.