Iterative double cyclization reaction by S_RN1 mechanism. A theoretical interpretation of the regiochemical outcome of diazaheterocycles

Abstract

In this report, we present a synthetic and mechanistic study of novel iterative double cyclization intramolecular S RN 1 reactions from diamides bearing two aryl iodide moieties. This cyclization affords aromatic diazaheterocyclic compounds in good yields. Two synthetic strategies were employed for their preparation: intramolecular S RN 1 and Homolytic Aromatic Substitution. The mechanism is non-trivial and we propose that radicals are intermediates. The regiochemistry was studied using computational calculations, employing the DFT method and B3LYP functional. It was found that the distribution of products depends on the cyclization activation energies, proportion of neutral conformers, and the type of the electron transfer reaction.

Construction of 3,3'‐Bicarbazoles and Indolocarbazoles by Using Visible Light

“…This behavior was also reported in the double cyclization reaction of diarylbenzylamines to give benzo[f]isoquinolino [3,4-b][1,8]naphthyridine and 6aHbenzo [5,6][1,8]naphthyridino [1,2-a]quinazoline. [49] Summarizing, this methodology avoids the use of palladium catalysts and ligands, toluene as solvent and high temperatures, previously described in the synthesis of 9 e and 9 e', where these compounds are obtained in 25 % yield. [50] Cl DMSO, KO t Bu (6 equiv), 1 h 51 [d] [a] Reactions were carried out under N 2 atmosphere using 5 a (1 equiv, 6.7 × 10…”

“…, 258 (13), 257 (19), 256 (30), 255 (12), 181 (12), 168 (12), 167 (82), 166 (27), 154 (15), 139 (12), 129 (33), 128 (49), 127 (12), 77 (10), 76 (13), 75 (12), 63 (13). FTIR (cm 24), 420 (11), 419 (M + , 48), 417 (26), 341 (19), 340 (98), 339 (22), 338 (100), 259 (22), 258 (62), 257 (16), 168 (12), 157 (53), 156 (20), 155 (12), 130 (11), 129 (64), 128 (24), 115 (12), 77 (24), 76 (18), 75 (17), 65 (11), 51 (11).…”

“…[46][47][48] It is worth noting in the literature there is a reported example of double ring closure reactions by S RN 1 where two 6membered rings are formed. [49] In this case, the photostimulated reaction in liquid ammonia of the bis(2iodobenzyl)benzene-1,4-diamine 2 was reported to give two isomeric products: dibenzo[a,k][4,7]phenanthroline 3 and isoquinolino [3,4-b]phenanthridine 4, by two intramolecular consecutive S RN 1 (Scheme 2, eq 1). With this in mind, and taking into account that carbazole-based structure is useful in optoelectronic materials and many structural variations are needed, in the present article we report a double cyclization reaction to afford 3,3'-bicarbazole from diarylamines using only base and visible light at room temperature (Scheme 2, eq 2).…”

Photochemical Synthesis of Azaheterocycles

“…An iterative double photocyclization was reported by Pierini and Buden. 49 As shown in Scheme 49, reaction of the diamine starting material with t-BuOK in liquid ammonia with irradiation (400 W high-pressure lamp) initiated an S RN 1 process to give a mixture of diphenanthridines 20 (46%) and 21 (25%), after oxidation of the photoproducts with MnO 2 . Other minor products obtained in the reaction were the monocyclization product and its reductively deiodinated or debenzylated adducts.…”

Photoinduced Synthesis of Dibenzofurans: Intramolecular and Intermolecular Comparative Methodologies

“…The S RN 1 mechanism has clearly manifested to be useful for obtaining heterocyclic compounds . Recently, the S RN 1 reaction was applied to form new C–C bonds in the synthesis of heterocycles such as phenanthridines and benzophenanthridines, phenanthrolines, 1-phenyl-1-oxazolyl-Indane derivatives, cyclopenta-oxazolo-isoquinolin-6-ones carbazoles and carbolines, , pyrrole, indole, and pyrazole fused azaheterocycles . The formation of C-heteroatom bonds is also reported as a consequence of an intramolecular cyclization to generate compounds such as 9 H -carbazoles, among others.…”