Synthesis of 5‐Substituted Benzo[h]quinoline Derivatives via Reactions Involving C(sp²)−Br Bond Activation

Abstract

In view of literature reports, benzo [h]quinoline and its substituted analogues, due to their structural similarity to 2-phenylpyridine derivatives, appear to be very promising C,N-cyclometalating ligands for iridium-based Phosphorescent Organic Light Emitting Diode technology. 5-bromo-benzo[h]quinoline aroused our particular interest as a convenient precursor for further transformations, and was successfully functionalized in the course of transition metal-promoted exclusive CÀC, CÀO and CÀN bond formation, yielding a series of 5-substituted benzo[h]quinoline derivatives with unique structures and properties. Some of the synthesized compounds seemed to be appropriate starting materials for subsequent transformations, and enabled the preparation of new benzo[h]quinoline-based materials, for instance those with fluorine or silsesquioxane groups, which have not been synthesized by the conventional Scraup protocol. In selected transformations, the assistance of microwave irradiation as a non-conventional energy carrier significantly improved efficiency, leading to the formation of desired products with yields of up to 99%.

Microwave-Accelerated C,N-Cyclometalation as a Route to Chloro-Bridged Iridium(III) Binuclear Precursors of Phosphorescent Materials: Optimization, Synthesis, and Studies of the Iridium(III) Dimer Behavior in Coordinating Solvents

“…Of particular interest was bzqH , a ppyH analogue, which seemed to be a potentially attractive C,N-donating ligand for the iridium dopant system because of its geometric similarity, more rigid structure, and extended electron conjugation system. Indeed, iridium­(III) complexes bearing nonfunctionalized bzq in the coordination sphere have shown interesting electroluminescent properties, which made them potentially useful in OLED technology, as evidenced by us and other groups. ,,, The preparation of [Ir­(μ-Cl)­(bzq) 2 ] 2 according to the methodology developed here proved to be very efficient; therefore, we focused on the synthesis of new iridium­(III) dimers using bzqH derivatives previously synthesized and characterized in our group . As a result, we obtained a series of new bzq-based chloro-bridged iridium­(III) dimers equipped with various functional groups (Scheme ).…”

“…34,37,39,44 The preparation of [Ir(μ-Cl)(bzq) 2 ] 2 according to the methodology developed here proved to be very efficient; therefore, we focused on the synthesis of new iridium(III) dimers using bzqH derivatives previously synthesized and characterized in our group. 38 As a result, we obtained a series of new bzq-based chloro-bridged iridium(III) dimers equipped with various functional groups (Scheme 2). The scope of the substituents included electron-donating groups (−OMe and −OPh), electron-withdrawing groups (−Br and −C 6 F 5 ), and p-type semiconducting moieties such as −NPh 2 and −C 6 H 4 NPh 2 .…”

“…We are convinced that the knowledge gained on this subject will be extremely useful for those researchers who want to improve the efficiency of their syntheses and to obtain both known and novel dimers with high yields, as shown here. Recently, we have published results on efficient stoichiometric and catalytic methods for the synthesis of various 5-substituted benzo­[ h ]­quinolines via C­( sp 2 )–Br bond activation . The ability of unmodified benzo­[ h ]­quinoline ( bzqH ) to cyclometalate iridium­(III) has already been confirmed per analogiam to 2-phenylpyridine ( ppyH ). , However, in contrast to countless complexes based on the ppy motif, only several examples of iridium­(III) complexes with bzq have been synthesized and characterized as potential electroluminescent phosphors.…”

Highly efficient microwave synthesis of rhodanine and 2-thiohydantoin derivatives and determination of relationships between their chemical structures and antibacterial activity

“… 47–49 During our thorough literature review, we encountered the promising concept of microwave-accelerated Knoevenagel condensation. 50 Because this unconventional heat source has recently been proved to increase the efficiency of various catalytic and stoichiometric reactions in our group, 51 we decided to examine its effectiveness in our current work. Preliminary tests in which anthracene-9-carbaldehyde and rhodanine were involved as a model reagent system confirmed the superior efficiency of microwave irradiation compared to a classical oil bath.…”

An efficient 3-acylquinoline synthesis from acetophenones and anthranilviaC(sp3)–H bond activation mediated by Selectfluor

“…[12][13][14] The synthesis of quinolines has been an active area for many years and as a result, a number of efficient synthetic methods have been developed, [15][16][17][18][19][20] such as the classical Skraup, [21][22][23] Combes, [24][25][26] Friedlander, [27][28][29] Gould-Jacobs, [30][31][32] and Doebner-von Miller reactions. [33][34][35][36] More recently, alternative strategies for the quinoline synthesis such as domino cycloadditions [37][38][39][40][41] and transition-metal mediated methods [42][43][44][45] have been introduced. However, most of the existing methods necessitate the use of strong acid or base conditions, high reaction temperatures, the use of expensive/toxic metal catalysts and frequently require the use of expensive, highly functionalized starting materials.…”