A Convenient and General Method for the Synthesis of Indole‐2,3‐dicarboxylates and 2‐Arylindole‐3‐carboxylates

Abstract

A transition-metal-free, simple and efficient one-pot method for the synthesis of indole-2,3-dicarboxylates and 2-arylindole-3-carboxylates is described. The corresponding products are obtained by a domino hydroamination/Fischer indole cyclization in good-to-excellent yields from easily

Photochemistry of Benzotriazoles: Generation of 1,3-Diradicals and Intermolecular Cycloaddition as a New Route toward Indoles and Dihydropyrrolo[3,4-b]Indoles

“…A yellow oil (126 mg) from column chromatography using ethyl acetate/pet. ether (1:1, R f = 0.58), MS: ( m/z , %) = 275 (M + , 80), 230 (35), 202 (95); NMR δ H (400 MHz, CDCl 3 ) 8.14 (d, 1H, J = 7.6), 7.38–7.36 (m, 2H), 7.32–7.28 (m, 1H), 4.48 (q, 2H, J = 7.2), 4.38 (q, 2H, J = 7.2), 3.84 (s, 3H), 1.44 (t, 3H, J = 7.2), 1.41 (t, 3H, J = 7.2); δ C (100 MHz, CDCl 3 ) 164.3, 163.1, 136.9, 135.2, 125.6, 124.5, 122.7, 122.5, 110.3, 108.1, 62.5, 60.4, 31.6, 14.6, 14.3; HR-MS (EI) m/z [M] + calcd for C 15 H 17 NO 4 275.1158, found 275.1153 [28].…”

Recent advances in the synthesis of indoles from alkynes and nitrogen sources

“…303 The authors discussed the structures of zinc intermediates and concluded that the key intermediate could be a dimeric structure, where the ZnCl 2 group is coordinated to the indole π-system to form a zwitterion, with the C3-carbon being tetrahedral and the C2carbon being trigonal. The domino alkyne-amination-Fischerindole sequence was described for the preparation of indole- 2,3-dicarboxylates, 304 2-methyl-3-substituted-indoles 305 and 2-methyl-3-amino-indoles. 306 The method was based on the reaction of phenylhydrazines with terminal or internal alkynes promoted by ZnCl 2 , ZnBr 2 , or Zn(OTf ) 2 affording the indole derivatives 235 (Scheme 273).…”

Transition Metal‐Catalyzed Synthesis of Fused Five‐Membered Aromatic Heterocycles

“…Later, Beller elaborated on the Ti(IV)-catalyzed hydrohydrazination-Zn(II)-promoted Fischer cyclization en route to tryptophols, their homologs [257], and 3-silyloxyindoles [258]. The same group performed a general study of the Ti(II)-catalyzed version of this reaction, and later investigated the Zn(II)-mediated synthesis of indole-2,3-carboxylates [259]. A substantially improved scope of this reaction in the case of terminal alkynes was achieved when stoichiometric amounts of Zn(II) triflate were used to promote both amination and indole ring formation processes [260].…”