Direct construction of carbazoles from 2-methyl-indole-3-carbaldehydes and enals

Abstract

The direct and rapid construction of carbazoles was achieved based on the reaction of 2-methyl-indole-3-carbaldehydes and enals promoted by the Lewis acid LiCl and DBU in a single operation.

Facile Synthesis of Polysubstituted Indolizines via One‐Pot Reaction of 1‐Acetylaryl 2‐Formylpyrroles and Enals

“…[4+2] annulation has proven as one of the most powerful and reliable strategies for the construction of structurally diverse six‐membered rings from simple raw materials . Recently, we have developed the direct and rapid construction of carbazoles via oxidative [4+2] annulation of 2‐methyl‐indole‐3‐carbaldehydes with enals promoted by LiCl/DBU in a single operation . As part of our ongoing interest in the synthesis of carbo‐ and heterocycles, we envisaged a novel strategy for the synthesis of highly functionalized indolizines might be achieved via oxidative [4+2] annulation of 1‐acetylaryl 2‐formylpyrroles and enals.…”

“…[12] As part of our ongoing interest in the synthesis of carbo-and heterocycles, [13] we envisaged an ovel strategy for the synthesis of highly functionalized indolizines might be achieved via oxidative [4+ +2] annulation of 1-acetylaryl 2-formylpyrroles and enals. Solventc oncentration investigation indicated that 2.0 mL is proper, generating 5, 6-dihydroindolizine 3a in up to 89 %y ield with 17:1 dr (entries [12][13][14][15]. Notably,Z ou group reported "one-pot" multicomponent methodt oi ndolizines and pyrido[1,2-a]indoles via pyridine-ring construction.…”

“…[11] Recently,w ehave developed the direct and rapid construction of carbazoles via oxidative [4+ +2] annulation of 2-methyl-indole-3carbaldehydes with enals promoted by LiCl/DBU in asingleoperation. [12] As part of our ongoing interest in the synthesis of carbo-and heterocycles, [13] we envisaged an ovel strategy for the synthesis of highly functionalized indolizines might be achieved via oxidative [4+ +2] annulation of 1-acetylaryl 2-formylpyrroles and enals. In fact, retaining the highly reactive formyl moiety under basic and oxidative conditions is one of main challenges for this strategy.H erein, we present the successful development of one-pot synthetic route to indolizines based on the formal [4+ +2] annulation of 1-acetylaryl 2-formylpyrroles with enals, followed by oxidative aromatization.…”

“…Then, base screening indicated that DBU was the bestc hoice (entries1-6), leading to the formation of 5, 6-dihydroindolizine 3a in 32 %y ield with > 20:1 dr.S ubsequently,s everals olvents werei nvestigated, with CHCl 3 provingt ob et he best choice in terms of yield and dr (entries 7-11). Solventc oncentration investigation indicated that 2.0 mL is proper, generating 5, 6-dihydroindolizine 3a in up to 89 %y ield with 17:1 dr (entries [12][13][14][15]. In the absence of LiCl, product yield and dr dramatically dropped (entry 16), indicating that Lewis acid [14,15] LiCl plays ac ritical role in this annulation.…”

Efficient synthesis of polyfunctionalized carbazoles and pyrrolo[3,4-c]carbazoles via domino Diels–Alder reaction

“…On the other hand, carbazole derivatives also have potential applications in optoelectronic materials, conducting polymers, and synthetic dyes [9][10][11]. Over the past decades, many efficient synthetic methodologies for functionalized carbazole derivatives have been successfully developed [12][13][14][15][16][17][18]. Because indoles are readily available materials, the direct extension of indoles to carbazole skeletons has a great advantage [19][20][21][22][23][24][25][26][27].…”