Diaroyl‐S,N‐ketene Acetals: Red‐Shifted Solid‐State and Aggregation‐Induced Emitters from a One‐Pot Synthesis

Abstract

Symmetric and unsymmetric diaroyl‐S,N‐ketene acetals can be readily accessed in consecutive syntheses in good to excellent yields by exploiting the inherent nucleophilic character of the methine position. Different aroyl‐S,N‐ketene acetals as well as acid chlorides yield a library of 19 diaroyl compounds with substitution and linker pattern‐tunable emission properties, leading to a significant red‐shift of emission in solid and aggregated state which were thoroughly investigated. Additionally, the stability of the luminescent aggregates is highly increased. In a follow‐up one‐pot procedure, pyrazolo‐S,N‐ketene acetals can easily be accessed employing a nucleophilic cyclocondensation.

Aroyl‐S,N‐Ketene Acetals: Luminous Renaissance of a Class of Heterocyclic Compounds

“…Synthesis of diaroyl-S,N-ketene acetals via a secondary additionelimination reaction, overview of investigated properties of diaroyl-S,Nketene acetals and Knorr pyrazole synthesis in a single step and in a one-pot procedure as a follow-up reaction. [80] Figure 8. Syntheses of fused aroyl-S,N-ketene acetals starting from benzothiazoles and 4-hydroxycoumarins by ball milling and overview of the investigated properties.…”

“…Consequently, for the 7 th generation, the inherent nucleophilicity of the methine position in the presence of an excess of base should be exploited (Figure 7). [80] This reaction principle is employed to open the substance class of diaroyl-S,N-ketene acetals by adding a significant excess of base. In this way, symmetrical derivatives are obtained starting from the respective benzothiazolium salts and acid chlorides.…”

“…By choosing an N-carboxyethyl-substituted benzothiazole derivative, an intramolecular nucleophilic attack even allows for the construction of a cyclized aroyl-S,N-ketene acetal (Figure 7, top). [80] Intramolecular cyclization using benzoyl chloride and Ncarboxyethyl benzothiazolium bromide allows for the further development of aroyl-S,N-ketene acetals into the pyrazolo-S,Nketene acetal class of compounds by reacting the cyclized product with an excess of hydrazine in a Knorr pyrazole synthesis. This reaction can be carried out both in a single-step procedure with intermediate isolation of the cyclized aroyl-S,Nketene acetal, giving an N-methylated and an N-benzylated derivative in yields of 74 and 39 %, respectively, and in a onepot procedure, giving N-phenyl pyrazolo-S,N-ketene acetal in a 50 % yield (Figure 7, bottom).…”

“…This reaction can be carried out both in a single-step procedure with intermediate isolation of the cyclized aroyl-S,Nketene acetal, giving an N-methylated and an N-benzylated derivative in yields of 74 and 39 %, respectively, and in a onepot procedure, giving N-phenyl pyrazolo-S,N-ketene acetal in a 50 % yield (Figure 7, bottom). [80] Inspired by the work on different generations of N-benzyl aroyl-S,N-ketene acetals consisting of a benzothiazole core, a simple and novel method for the synthesis of fused aroyl-S,Nketene acetals by direct coupling of benzothiazole salts and 4hydroxycoumarins under mechanochemical conditions has been developed by Chen and coworkers. By varying the substituents on both the coumarin and the benzothiazole core, a variety of solid-state emitters can be obtained in mediocre to very good yields.…”