Active Ester Functionalized Azobenzenes as Versatile Building Blocks

Abstract

Azobenzenes are important molecular switches that can still be difficult to functionalize selectively. A high yielding Pd-catalyzed cross-coupling method under mild conditions for the introduction of NHS esters to azobenzenes and diazocines has been established. Yields were consistently high with very few exceptions. The NHS functionalized azobenzenes react with primary amines quantitatively. These amines are ubiquitous in biological systems and in material science.

In‐situ Oxidation and Coupling of Anilines towards Unsymmetric Azobenzenes Using Flow Chemistry

“…This specific substitution pattern enables to perform two selective cross-couplings with a minimal loss of selectivity. [26] At first, the synthesis was done with the same conditions reported above. However, the target azobenzene crushed out in the second reactor causing a blockage in the flow set-up.…”

“…Finally, an asymmetric azobenzene containing two different halides was targeted as a modular building block for the synthesis of larger azobenzene‐containing systems (Figure 4, 3 w ). This specific substitution pattern enables to perform two selective cross‐couplings with a minimal loss of selectivity [26] . At first, the synthesis was done with the same conditions reported above.…”

Synthesis of a Series of 12-Membered Azobenzene Macrocycles and Tuning of the Half-Life of the Thermal Z–E Isomerization

“…In general, postsynthesis, ortho functionalizations are difficult to achieve with cross-coupling routes, and different synthetic strategies have to be employed. 22 Compound 3 was used to find optimum reaction conditions for Suzuki cross-coupling reactions (different solvents, bases, catalysts, and temperatures) with a tolylboronic acid as a nucleophilic cross-coupling partner (Table 1). The reactions were monitored by NMR spectroscopy.…”

“…The syntheses of meta- and para -bromo-substituted 12-membered AzMs were achieved similarly as described in our previous contribution on the unsubstituted AzM to obtain overall yields of 46 and 47%, respectively (Scheme ). In general, postsynthesis, ortho functionalizations are difficult to achieve with cross-coupling routes, and different synthetic strategies have to be employed . Compound 3 was used to find optimum reaction conditions for Suzuki cross-coupling reactions (different solvents, bases, catalysts, and temperatures) with a tolylboronic acid as a nucleophilic cross-coupling partner (Table ).…”

Stille vs. Suzuki – cross-coupling for the functionalization of diazocines

“…However, one common tool in organic chemistry for late-stage functionalization, namely cross-coupling reactions, has only been used sporadically, with diazocine as the formally electrophilic component. 4 a ,8 a ,11 and one single example with a stannylated diazocine. 12 In those examples, the cross-coupling reactions were not further investigated (Scheme 1a).…”