Stannous Chloride-Mediated Reductive Cyclization−Rearrangement of Nitroarenyl Ketones

Abstract

Cyclization products are produced in excellent yields from using standard reaction conditions for nitroarene reduction to aminoarene with SnCl2. Thus, 4-methyl-2-(2-nitrobenzyl)-2H-1,4-benzothiazin-3(4H)-one (2b) upon treatment with SnCl2 in ethanol did not produce the expected aniline derivative. Instead, 6-methyl-11a, 12-dihydro-6H-quino[3,2-b][1,4]benzothiazine (3) was produced in excellent yield, presumably via novel Sn (IV)-mediated amidine formation from the initial aniline reduction product. Under identical reaction conditions, 2-(2-nitrophenyl)-thiochroman-4-one (6) produces ethyl 5,11-dihydrodibenzo[b,e][1,4]thiazepin-11-ylacetate (7). A novel semipinacol rearrangement is proposed to account for this extensive skeletal rearrangement. Aniline derivative (14) (from 6 treated with FeSO4.7H2O) forms 12-ethoxy-11,12-dihydro-6H-6,12-methanodibenzo[b,f][1,5]thiazocine (15) upon treatment with SnCl2 in ethanol. Thiophene analogues of 6 and 14 (18 and 19, respectively) react similarly, forming the analogous thiazepine (20) and cyclic N,O-acetals (21), respectively.

Synthesis and Evaluation of Thiochroman-4-One Derivatives as Potential Leishmanicidal Agents

“…Thus, strong dehydrating agents, such as sulfuric, methanesulfonic or p-toluenesulfonic, only gave trace amounts of the expected product; additionally, formation of the respective acid chloride, followed by intramolecular Friedel-Crafts acylation with aluminum trichloride, also failed. Finally, the synthetic procedure was performed according to Bates and Li [ 21 ], and thioflavanone was prepared from the acid chloride of 3-phenyl- 3-(phenylthio)-propanoic acid using tin(IV) chloride as a Lewis acid catalyst, with moderate yields. The same method worked well for the preparation of other thioflavanones.…”

Functionalized Benzimidazole Scaffolds: Privileged Heterocycle for Drug Design in Therapeutic Medicine

“…SnCl 2 ·2H 2 O is popularly used to selectively reduce aromatic nitro group to amino for its eco‐friendly nature, affordability, high reactivity, and safety profile . Regarding the mechanism of the reductive cyclization reaction process, Duan and coworkers speculated that 2‐amino‐5‐substituted aniline, Schiff base intermediate, was formed first through SnCl 2 .…”

SnCl2/EtOH-Mediated Synthesis of Novel 4-Ethoxy- and 4-Chloroindazoles Bearing Sulfonamide Moieties

“…In view of its inherent properties such as reusability, greater selectivity, operational simplicity, non-corrosiveness, low cost and ease of isolation, several groups have accomplished efficient syntheses of different heterocyclic compounds employing the reduction of nitro derivatives with stannous chloride [6][7][8][9] . Our research program during the last ten years has been focused on the synthesis of heterocyclic compounds using anhydrous SnCl 2 as reductive reagent [10][11][12][13][14][15][16][17] .…”