Synthesis and Properties of Aza‐ullazines

Abstract

A range of aza-ullazines, which represent a new heterocyclic core structure, were synthesized through a scalable four-step reaction, including a Sonogashira reaction and metal-free cyclization promoted by p-toluenesulfonic acid. The optical and electrochemical properties of selected derivatives were investigated, they were found to have similar absorption and emission spectra but a higher oxidation potential than the parent ullazine core.

Controlling charge-transfer properties through a microwave-assisted mono- or bis-annulation of dialkynyl-N-(het)arylpyrroles

“…19 Next, a Sonogashira cross-coupling reaction was selected to prepare compounds 4a-c. Previous reports used either P( t Bu) 3 13 or di-1-adamantyl-n-butylphosphine (cataCXium® A) 18 as oxygen sensitive phosphines for 24 hours as reaction time. In our case, we optimized the reaction conditions using standard PdCl 2 (PPh 3 ) 2 /CuI and the less air sensitive PPh 3 as catalytic system, together with microwave irradiation as heating source.…”

“…16,17 Recently, Boldt et al reported on the synthesis of aza-ullazine derivatives in a metal-free cyclization promoted by ptoluenesulfonic acid for the first time. 18 However, the presence of an additional nitrogen atom on the periphery did not lead to any noticeable modification of the photophysical properties in comparison with parent ullazine derivatives.…”

“…, 2b and 2d were prepared according to previously reported procedure. 24 Pyrroles 3a, 13 3b 15 and 3d 18 have been described previously. Sonogashira coupling procedures were adapted from literature.…”

“…13 However, similarly to most PAHs, nonderivatized (aza-)ullazines present rather apolar photophysical features corresponding mainly to local electronic transitions. 10,13,18 Nevertheless, a better charge transfer character could be induced by breaking the symmetry of the Please do not adjust margins Please do not adjust margins system as it would be, for example, in the case of ullazineprecursor mono-annulated N-(het)arylpyrroles.…”

Pyridinic Nanographenes by Novel Precursor Design

“…Overall, the synthesis and purification of 4 b was easier compared to 4 a . The pyridinic half of the molecule with the pre‐formed bonds at the 3/5 positions was prepared starting from 4‐aminopyridine which was brominated with N ‐bromosuccinimide (NBS) via standard procedures [15] . The obtained di‐brominated derivative 6 was then subjected to Suzuki couplings either with phenylboronic acid for 7 a or with 3‐ tert ‐butylphenylboronic acid for 7 b .…”