Catalytic copper-mediated ring opening and functionalization of benzoxazoles (original) (raw)
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The Journal of Organic Chemistry, 2013
A one-pot protocol for the synthesis of 1,2,3triazoles has been developed starting from inactivated alkenes and based on two click reactions: the azidosulfenylation of the carbon−carbon double bond and the copper-catalyzed azide− alkyne cycloaddition (CuAAC). High yields of the βmethylsulfanyl triazoles have been attained using CuNPs/C as catalyst, with other commercial copper catalysts being completely inactive. The versatility of the methylsulfanyl group has been demonstrated through a series of synthetic transformations, including direct access to 1-vinyl and 4-monosubstituted triazoles. C lick chemistry has become one of the most important concepts in modern chemistry. 1 It represents certain highly efficient and reliable reactions which are modular, wide in scope, high yielding, stereospecific, and proceed under simple and benign conditions with straightforward procedures for product isolation. Recently, click chemistry's first decade has been celebrated, 2 with an endless list of disciplines having benefited from the unique advantages offered by this type of reaction. The copper-catalyzed azide−alkyne cycloaddition (CuAAC) 3 fulfills the aforementioned series of rigorous criteria, as defined by Sharpless et al., turning this reaction into the click reaction by antonomasia. 4 The nucleophilic opening of springloaded rings (i.e., epoxides, aziridines, cyclic sulfates, cyclic sulfamidates, aziridinium ions, and episulfonium ions) also belongs to the privileged list of click reactions because they are reliable, stereospecific, often highly regioselective, and nearly quantitative. 1 The CuAAC has been traditionally implemented with preformed organic azides. More advantageous are, however, the methodologies in which the organic azides are generated in situ from organic halides 5 (three-component azide−alkyne cycloaddition) because (a) hazards derived from their isolation and handling are minimized, (b) time-consuming and wastegenerating additional synthetic steps are avoided, and (c) the common organic solvents utilized (e.g., dioxane, toluene, DMF, dichloromethane, and hexane) can be replaced by neat water. In this vein, efforts have been recently devoted to develop new catalytic systems which allow the CuAAC from other azide precursors, namely amines, 6 tosylates, 7 diarylidodonium salts, 8 epoxides, 9 alcohols, 10 and boronic acids. 11 Favi et al. reported the one-pot copper(II)-catalyzed aza-Michael addition of trimethylsilyl azide to 1,2-diaza 1,3-dienes and copper(I)catalyzed 1,3-dipolar cycloaddition of the in situ generated αazido hydrazones with alkynes. 12 However, alkenes are the 51 most commonly available starting materials which can provide a 52 carbon framework. To the best of our knowledge, the synthesis 53 of 1,2,3-triazoles from inactivated alkenes has never been 54 described. 55 On the other hand, there is an upsurge of interest in the use 56 of nanostructured copper catalysts for CuAAC because of their 57 large surface-to-volume ratio, varied morphology, and sustain-58 able catalytic applications. 13 Owing to our dedication to study 59 and understand the reactivity of metal colloids, 14 we found out 60 that active copper [obtained from CuCl 2 •2H 2 O, lithium metal, 61 and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB) in 62 THF at room temperature] was able to reduce different organic 63 functionalities under very mild conditions. 15 We also 64 discovered that copper nanoparticles (CuNPs) are formed 65 when the active copper is generated from anhydrous CuCl 2 66 under the above-mentioned conditions. These unsupported 67 copper nanoparticles (10 mol %) effectively catalyzed the 68 CuAAC in the presence of triethylamine at 65°C in THF. 16 69 Remarkably short reaction times (10−120 min), comparable to 70 those previously reported under microwave heating, were 71 recorded in the absence of any stabilizing additive or ligand. 72 Unfortunately, the CuNPs underwent dissolution under the 73 reaction conditions which precluded their reuse. More recently, 74 we introduced a catalyst consisting of oxidized copper 75 nanoparticles on activated carbon (CuNPs/C), readily 76 prepared under mild conditions, which exhibited a high 77 versatility in the multicomponent click synthesis of 1,2,3-78 triazoles in water. 17 Not only organic halides but diazonium 79 salts, anilines, and epoxides were successfully used as azide 80 s1 precursors in the CuAAC (Scheme 1). We want to present 81 herein the first one-pot transformation of inactivated olefins
ACS Combinatorial Science, 2019
Glycosyl triazoles are conveniently accessible and contain multiple metal-binding units that may assist in metal-mediated catalysis. Azide derivatives of D-glucose have been converted to their respective aryltriazoles and screened as ligands for the synthesis of 2-substituted benz-fuzed azoles and benzimidazoquinazolinones by Cu-catalyzed intramolecular Ullmann type Cheteroatom coupling. Good to excellent yields for a variety of benz-fused heterocyles were obtained for this readily accessible catalytic system.
Advanced Synthesis & Catalysis, 2004
The solvents used were purified by distillation over the drying agents indicated and were transferred under Ar: tetrahydrofuran (THF) (Na), CH 2 Cl 2 (P 4 O 10), MeCN, Et 3 N, pyridine, NMP, hexamethylphosphoramide (HMPA), tetramethylethylenediamine (CaH 2), dimethylformamide (DMF) (dibutyltin dilaurate/Desmodur), MeOH, EtOH (Mg), and toluene (Na/K). For flash chromatography, Merck silica gel 60 (230-400 mesh) was used. For NMR, spectra were recorded on a DPX 300 or AV 400 spectrometer (Bruker) in the solvents indicated; chemical shifts (δ) are given in parts per million relative to tetramethylsilane, and coupling constants (J) are given in hertz. For IR, a Nicolet FT-7199 spectrometer or Perkin-Elmer Fourier transform-IR Diamant Spectrum One (ATR) was used; wavenumbers (ν) are given in cm-1. For MS [electron ionization (EI)], a FinniganMAT 8200 (70 eV) was used, and for high-resolution MS (HRMS), a Finnigan MAT 95 was used. All commercially available compounds were used as received. General procedure I for the cyclization of 2-bromobenzamides (Scheme 3): 2-Bromobenzamide (1.0 mmol), K 2 CO 3 (276 mg, 2.0 mmol) and CuI (10 mg, 0.05 mmol) were weighed into a vial under air. The vial was evacuated and filled with argon, followed by the addition of N,N'-dimethylethylenediamine (11 µL, 0.1 mmol) and toluene (3 mL). The vial was sealed and the reaction mixture stirred at 110 °C for 24 h. After cooling to rt the reaction mixture was poured into 25% aqueous NH 4 OH, extracted with EtOAc, dried over Na 2 SO 4 , filtered and
Asian Journal of Chemistry, 2013
The ever increasing demand for the novel medicinally active compounds and the laborious process of lead discovery and optimization have resulted in the continuous search for simple and efficient methods for generation of libraries for biological screening. Click chemistry has emerged as a fast and efficient approach to synthesize novel compounds with desired function making use of selected "near perfect" reactions 1. The Huisgen 1,3-dipolar cycloaddition 2 of azides and alkynes resulting in 1,2,3-triazoles is one of the most powerful click reactions. Copper catalyzed ligation of organic azides and terminal alkynes has enjoyed much use since its discovery. Exclusive regioselectivity, wide substrate scope, mild reaction conditions and very high yields 3 have made it the method of choice for making permanent connections by means of 1,4-disubstituted 1,2,3-triazoles. Since then, this reaction has been used for the construction of a variety of multivalent structures such as sugar heterodimers, glycoconjugates 4 , calix-sugars 5 and dendritic and polymeric materials 6. Furthermore, the one-pot multistep reaction involving the Wittig olefination, the Knoevenagel condensation, the Diels-Alder cyclization and Cu(I)-catalyzed alkyne-azide coupling has been explored 7. Gratifyingly, the same level of success has been found when compared to the traditional methodology. In another variation, microwaveassisted one-pot reaction has generated a variety of triazoles directly from activated aryl halides and sodium azide 8. In a similar fashion, taking advantage of anomeric activation, rapid
Advanced Synthesis & Catalysis, 2010
Copper nanoparticles on activated carbon have been found to effectively catalyse the multicomponent synthesis of 1,2,3-triazoles from different azide precursors, such as organic halides, diazonium salts, anilines and epoxides in water. The first one-pot transformation of an olefin into a triazole is also described. The catalyst is easy to prepare, very versatile and reusable at a low copper loading.
Scientific Reports
A single pot, wet chemical route has been applied for the synthesis of polymer supported copper azide, CuN3, nanoparticles (CANP). The hybrid system was used as ‘catalyst-cum-reagent’ for the azide-alkyne cyclo-addition reaction to construct triazole molecules using substituted benzyl bromide and terminal alkyne. The electron donating group containing terminal alkyne produced 5-alkynyl 1,4-disubstituded triazole product whereas for alkyne molecule with terminal electron withdrawing group facilitate the formation of 1,4-disubstituted triazole molecule.
Research on Chemical Intermediates, 2017
The rapid method for the synthesis of organic azides was achieved by employing azide acceptors such as halides, epoxides and pseudohalides like diazonium salts and aryl boronic acids in hydrotropic media. In extension, the sequential multicomponent reaction of epoxides, azide and alkynes using copper catalysis has been discussed. The reaction proceeds via the in situ generation of azido-alcohol followed by synthesis of chiral b-hydroxytriazoles. This [3 ? 2] cycloaddition reaction of azide and alkyne using copper catalysis serves as a green and efficient protocol in ''Click Chemistry''. The nucleophilic addition of azide to epoxide and alkyne-azide cycloaddition is the two simultaneous regioselective click reactions observed in the proposed method.