1,3-Dipolar cycloaddition approach to isoxazole, isoxazoline and isoxazolidine analogues of C-nucleosides related to pseudouridine

Synthesis of Isoxazole and 1,2,3-Triazole Isoindole Derivatives via Silver- and Copper-Catalyzed 1,3-Dipolar Cycloaddition Reaction

“…Without catalyst, the targeted cycloadducts were only obtained in refluxing toluene, albeit in moderate amounts. The examination of the TLC of the reactions mixtures indicated the presence of only one product, which, after classical workup, was identified as cycloadducts 4 or 6 resulting from the thermal cycloaddition of the acetylene function and the 1,3-dipoles in accordance with the literature [44][45][46]. After optimization of the reactions conditions, we then performed all the cycloaddition reactions in presence of Ag 2 CO 3 (10 mol %) using the same protocol given above.…”

Nucleoside and nucleotide analogues by catalyst free Huisgen nitrile oxide–alkyne1,3-dipolar cycloaddition

“…Following oxidation and work-up, the protecting group was removed from 19 by treatment with DCA and 20 was obtained in 53% yield over the two steps, Scheme 3. Analysis by 31 P, 13 C and 1 H NMR spectroscopy together with HRMS data confirmed the expected structure. In particular a resonance at d -2.6 ppm is diagnostic for the P(V) nucleus; proton and 13 C assignments were supported by 2D-COSY experiments.…”

“…The LC/TOF-MS was a model 6210 Time-Of-Flight LC/MS (Agilent Corp, Santa Clara, CA) with an electrospray source positive and negative (ESI ±), capilary 3,500 V, nebuliser spray 30 psig, drying gas 5 L min -1 , source temperature 325 • C. The fragmentor was used at 175 V. Reference masses (Agilent solution) were 121.050873, 149.02332, 322.048121, 922.009798, 1221.990633, 1521.971475, and 2421.91399 m/z. The NMR spectra were obtained for 1 H at 300 MHz, for 13 C at 75 MHz and for 31 P at 121 MHz on a Bruker instrument at 25 • C. All samples for NMR were prepared in CDCl 3 . Chemical shifts are reported in ppm downfield from TMS as standard and coupling constants are reported in hertz.…”

Synthesis of 5-hetaryluracil derivatives via 1,3-dipolar cycloaddition reaction

“…azides, nitrones etc.,) has made this reaction a very powerful tool for the synthesis of 5-membered heterocyclic rings. [46][47][48][49][50][51][52][53][54] Several papers have described the formation of 5-(1,2,3-triazol-4-yl)uracil derivatives from 5-ethynyluracil and organic azides in the presence of CuI-sodium ascorbate catalytic system. [46][47][48][49][50][51] The formation of both possible regioisomers 1,4-and 1,5-disubstituted triazoles, depending on the applied catalyst, has been found.…”

“…The addition of nitrile oxides to 2'-deoxy-5-ethynyluridine was used in the construction of 5-(isoxazol-5-yl) derivatives. 52 The nitrile oxide and nitrones derived from 5-formyluracil were applied as 1,3-dipoles in construction of 5-hetaryluracils. 53,54 Other methods like Diels-Alder cycloaddition, cleavage of diazonium salts formed from 5-aminouracil in the presence of azoles have had limited application for single reactions only.…”