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Green Chemistry and Green Catalysts
Published in Ahindra Nag, Greener Synthesis of Organic Compounds, Drugs and Natural Products, 2022
Ahindra Nag, Himadri Sekhar Maity
Kirschning and co-workers reported35 newly developed multistep continuous flow synthesis process of olanzapine using inductive heating (IH) technology which reduces reaction times and increases process efficiency based on the induction of an electromagnetic field (at medium or high frequency depending on nanoparticle sizes). The synthetic step consisted of coupling aryl iodide and aminothiazole using Pd2dba3 as catalyst and xantphos as ligand and ethyl acetate as solvent. After quenching with distilled water and upon in-line extraction in a glass column, the crude mixture was passed through a silica cartridge in order to remove Pd catalyst. Nitroaromatic compound was then subjected to reduction with Et3SiH into a fixed bed reactor containing Pd/C at 40°C to get aniline. The product from the reactor was mixed with HCl (0.6 M methanol solution) and heated at 140°C to get the product with an overall yield of 88% (Figure 1.7).
The generation and reactions of sulfenate anions. An update
Published in Journal of Sulfur Chemistry, 2022
Adam B. Riddell, Matthew R. A. Smith, Adrian L. Schwan
In the preeminent paper involving arylation of sulfenate anions in terms of broad applicability of the optimized method, number of products, and yields/enantioselectivities of the products, Zhang and coworkers [56] attempted to find a set of universal conditions that could be utilized for enantioselective arylation of both alkyl and aryl sulfenate anions. Their research showed that when using a XantPhos type ligand bearing a chiral sulfinamide (Rc, Rs)−38 (Scheme 24), aryl benzyl sulfoxides with enantioselectivities up to 96% could be synthesized. The final optimized conditions illustrated in Scheme 24 were utilized by the researchers to synthesize 96 aryl alkyl sulfoxides from alkyl tert-butoxycarbonylethyl sulfoxides in yields ranging from 42 to 98% and e.e.’s (in favor of the R configuration) ranging from 86 to 99% (Scheme 24a) [56]. The researchers also synthesized 16 enantioenriched diaryl sulfoxides in yields ranging from 46 to 94% with e.e.’s ranging from 86 to 98% (Scheme 24b) [56].
Pd2(dba)3-catalyzed amination of C5-bromo-imidazo[2,1-b][1,3,4] thiadiazole with substituted anilines at conventional heating in Schlenk tube
Published in Journal of Sulfur Chemistry, 2021
Afterward, the reaction in entry 16 in Table 1 was optimized using Buchwald Hartwig amination under conventional heating. The optimization (Table 2) involved performing the reaction at different concentrations of Pd2(dba)3 with the catalyst, xantphos as the ligand, potassium carbonate, cesium carbonate, potassium tert-butoxide as different bases, under different solvents at different temperatures with and without inert conditions and reactions were monitored for a period of time. The optimized condition was used Pd2(dba)3 as the catalyst at 10 mol% conc., xantphos as the ligand at 20 mol% conc., cesium carbonate as the base at 2.5 eq. conc. in dry 1,4-dioxane under an inert atmosphere at 120°C for 14 h as shown in entry 8 of Table 2. The optimized reaction condition was then evaluated for substituted anilines (7a) with different electron-donating and withdrawing groups at the ortho, meta, and para positions for evaluation of the substrate scope of the method as shown in Figure 4. The advantages of the method are: (i) it can be used for the synthesis of imidazo[2,1-b][1,3,4]thiadiazol-5-(N-aryl)amine with moderately good yields (ii) it excludes microwave assistance by performing the reaction under an inert atmosphere in Schlenk tube, and (iii) electron-donating and electron-withdrawing groups at the ortho, meta and para positions are well tolerated.