Monoaza[5]helicenes. Part 2: Synthesis, characterisation and theoretical calculations

Azahelicenes and other similar tri and tetracyclic helical molecules

“…In order to complete the series of monoaza[5]helicenes, Caronna et al 6 revised their initial synthetic approach. As the final photocyclization step showed both high yields and regioselectivity, the method was applied on different key intermediates.…”

2,13-Diaza[5]helicene: synthesis, theoretical calculations and spectroscopic properties

“…2 Similar difficulties were anticipated in designing the photochemical synthesis of 2,13-diaza[5]helicene, and for this reason a non-photochemical approach was devised at first, but the overall yield was extremely low, 4 so as to call for a different approach.…”

“…2 we considered a "free valence" atomic index, analogous to the one introduced in the context of the Hückel model. 5a,b We examined the two possible conformations 6Z-a and 6Z-b: the first one with the pyridine ring oriented inwards, in a geometry close to (5), the second one with the pyridine ring oriented outwards, similar to (7) (Scheme 2).…”

“…1 In the past, we reported the synthesis of a certain number of monoaza 2,3 and diazahelicenes 3 , generally utilizing a photochemical approach.…”

“…2 The reason was that the photochemical ring closure of all possible precursors to this molecule, namely 7-(2-naphthalen-2-yl-vinyl)-isoquinoline (1), 4-(2-phenanthren-3-yl-vinyl)-pyridine (2) and 9-styryl-benzo[h]isoquinoline (3) all brought exclusively to the corresponding perylene (4) (Scheme 1) . …”