Sequential Cu‐Catalyzed Four‐ and Five‐Component Syntheses of Luminescent 3‐Triazolylquinoxalines

Abstract

3-Triazolylquinoxalines can be readily synthesized by applying two complementary synthetic protocols starting from heterocyclic p nucleophileso r( hetero)arylg lyoxylic acids in ac onsecutive four-or five-component reaction. Conceptually,t he sequential use of as ingle cuprous salt for alkynylation and Cu-catalyzed alkyne-azidec ycloaddition (CuAAC) in ao ne-pot fashion sets the stage for activation-alkynylation-cyclocondensation-CuAAC or glyoxylation-alkynyl-ation-cyclocondensation-CuAACs equences in good yields. The diversity-oriented generation of differently substituted 3-triazolylquinoxalines is an excellent entry to tunable emission solvatorchromic fluorophores with triazole ligation.T he electronic structure,c orroborated by DFT and TD-DFT calculations,r ationalizes the charge transfer character of relevant absorptions and large Stokes shifts as well as the electronic innocence of the triazole substituents.

Multicomponent and One‐pot Syntheses of Quinoxalines

“…DFT‐calculations revealed one of the quinoxaline nitrogen atoms to be the most likely protonation site (Scheme 21). [38–40] …”

“…Crystal structure analysis reveals a centrosymmetric pairwise arrangement by strong π‐π interactions between the triazolyl rings (Scheme 23). [39] …”

“… Synthetic approach to 3‐triazolylquinoxalines via five‐component glyoxylation‐alkynylation‐cyclo‐condensation‐CuAAC sequence (GACC‐CuAAC sequence, left), and four‐component activation‐alkynylation‐cyclo‐condensation‐CuAAC sequence (AACC‐CuAAC sequence, right) [39] …”

Recent advances in organic dyes and fluorophores comprising a 1,2,3-triazole moiety

“…Luminescent molecules can also be obtained using a complex procedure as exemplified in the following series of fluorophores. 91 Fourteen 3-triazolylquinoxaline derivatives 174-188 were notably prepared using a glyoxylation-alkynylation-cyclocondensation-Cu-catalyzed alkyne-azide cycloaddition (GACC-CuAAC) sequence requiring five components to proceed. In this one pot reaction, coupling glyoxylation of rich p-electron heterocycles, Castro alkynylation of acyl chlorides by alkynes, and cyclocondensation of diketones with diphenylamine followed by a click reaction of various azide derivatives 194-204 with alkynes 189-193 furnished 174-188 with reaction yields ranging from 42% for 178 to 82% for 174 (see Scheme 18).…”

“…Two photon absorption cross-sections d TPA and wavelength of the maximum TPA cross-section reported in ref 91. …”