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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Although 14-azacamptothecin was synthesized successfully, unfortunately no asymmetric induction was observed under Sharpless asymmetric dihydroxylation conditions, providing only the racemic product. The same result was reported using other chiral ligands like (DHQD)2-PHAL. The two proximal nitrogen atoms (N-1 and N-14) in the rigid cyclic enol ether might disrupt the coordination of osmium with the chiral ligand during the AD reaction. As an alternative, the enantioselective dihydroxylation was performed early in the synthesis (Scheme 51) to afford the oxygenated stereogenic center in 94% enantiomeric excess. Due to the poor regioselectivity observed in O- and N-propargylation step, it was decided to synthesize the O- and N-allyl mixture and perform a Pd-catalyzed rearrangement of O-allyl to N-allyl derivative. The rearrangement was successful and formed the key N-allyl amide in a remarkable yield of 100%. These allyl amides were not previously used in the aza-Diels-Alder cascade reaction designed earlier with alkyne tethers. The allyl amide was treated with 3 eq. triphenylphosphine oxide and 1.5 eq. Tf2O at 0 °C, followed by oxidation with freshly prepared manganese(IV) oxide to afford the pentacyclic intermediate in 89% yield. This conversion represented a novel application of the Hendrickson reagent where an allyl group underwent a highly efficient aza-Diels-Alder cascade reaction successfully. The enantioselective synthesis was completed upon deacetylation of pentacyclic intermediate with concentrated hydrogen chloride in C2H5OH to afford (S)-14-azacamptothecin in >99% enantiomeric excess and 95% yield [104].
Waste Production and Input Material Consumption
Published in John Andraos, Reaction Green Metrics, 2018
Expected mass of triphenylphosphine oxide produced in Wittig reaction = (x*0.1*278)*(1000/(x*0.1*96)) = 2895.83 g
An insight on the different synthetic routes for the facile synthesis of O/S-donor carbamide/thiocarbamide analogs and their miscellaneous pharmacodynamic applications
Published in Journal of Sulfur Chemistry, 2023
Faiza Asghar, Bushra Shakoor, Babar Murtaza, Ian S. Butler
The Staudinger-aza-Wittig reaction is quite useful and can be employed to make an extensive range of compounds. Though, it is challenging to remove triphenylphosphine oxide that is the consequence of this process. Polymer-bound diphenyl phosphine (PS-PPh2) is known to be capable of performing this reaction in a heterogenous system. In spite of higher reagent costs, using PS-PPh2 has the benefit of a significantly simpler reaction setup. Carnaroglio et al. [37] described a polymer regeneration technique, although the recycling step is unnecessary due to a quasi-stoichiometric quantity. They recently argued that the fabrication of triphenylphosphine-loaded cross-linked cyclodextrin complexes as recyclable green catalysts in an attempt to address cost effectiveness [37].
Efficient preparation of phosphazene chitosan derivatives and its applications for the adsorption of molybdenum from spent hydrodesulfurization catalyst
Published in Journal of Dispersion Science and Technology, 2022
Hala. A. Ibrahium, Bahig M. Atia, Nasser. S. Awwad, A. A. Nayl, Hend A. Radwan, Mohamed A. Gado
At the beginning adding 0.1 mol triphenylphosphine oxide (TPPO) to 0.1 mol AlCl3 hard Lewis acid in an suitable 50 mL of DMF in a condenser for 3 h at 50 °C. After that neutralization step was begins by adding 0.1 mol Sodium hydroxide, to 0.1 mole of thiosemicarbazide, in a suitable 50 mL of DMF as the diluent. The concerning mix was refluxed at 50 °C for 3 h. The main purpose of neutralization step is to increase the nucleophilicity of the Thiosemicarbazide. Finally, the two additives were added to each other with condensation for 8 h at 100 °C. The paper chromatography (PC) was used to monitor the reaction progress using PC sheets with Ethyl acetate + Ethanol 50:50 v/v as a solvent. The spots were seen with a UV lamp. The prepared PZEN appears as a crystalline glossy white solid with a density of ≈0.957 g/cm3. At the reaction end, the obtained PZEN was rinsed many times with distilled water to get rid of the residual DMF and AlCl3 (Scheme 1(A)).
Synthesis of helical branched carbodiimide polymers with liquid crystalline properties
Published in Liquid Crystals, 2022
Enosha Harshani De Silva, Bruce M. Novak
4.59 g (0.047 mol) of 5-hexyn-1-amine and 5.64 g (0.047 mol) of phenyl isocyanate were combined and allowed to react 8 h in dichloromethane. The obtained, white-coloured urea was recrystallised in ethanol. The corresponding white-coloured crystals were separated by filtration and dried under vacuum. To a round bottom flask, 100 mL of dichloromethane was combined with 2.50 g (5.78 mmol) of triphenylphosphine dibromide, 1.60 mL (11.57 mmol) triethylamine, and the 1.00 g (4.63 mmol) of synthesised urea at 0°C. The reaction was allowed to reach room temperature and monitored by IR (Infrared) spectroscopy, monitoring the appearance of a strong carbodiimide stretching peak at ~2140 cm−1. The reaction was quenched by adding n-hexane, and the solution was filtered to remove the byproducts of triphenylphosphine oxide and triethylammonium bromide salt. The filtrate was evaporated by rotary evaporation. The monomer was further purified by performing silica gel chromatography with dichloromethane as the mobile phase. Colourless thick liquid yield 90%. 1H NMR (500 MHz, CDCl3): δ (ppm) 7.32 (2H, d, Ar-H),7.13 (3 H, d, Ar-H), 3.49 (2 H, t, NCH2), 2.29 (2 H, td, CH2), 2.00 (H, t, CH),1.83 (2 H, p, CH2), 1.70 (2 H, p, CH2).