99-77-4Relevant articles and documents
Further characterization of mitsunobu-type intermediates in the reaction of dialkyl azodicarboxylates with P(III) compounds
Kumara Swamy,Praveen Kumar,Bhuvan Kumar
, p. 1002 - 1008 (2006)
Structural characterization of compounds analogous to the proposed intermediates in the Mitsunobu esterification process is achieved by the combined use of NMR spectroscopy and X-ray diffractometric studies. The results show that compounds (t-BuNH)P(μ-N-t-Bu)2P[(N-t-Bu)(N-(CO 2R)-N(H)(CO2R))] [R = Et (11), i-Pr (12)], obtained by treating [(t-Bu-NH)P-μ-N-t-Bu]2 (10) with diethylazodicarboxylate (DEAD) or diisopropylazodicarboxylate (DIAD), respectively, have a structure with the NH proton residing between the two nitrogen atoms ((P)N(t-Bu) and (P)N-N(CO2Et)); this is the tautomeric form of the expected betaine (t-BuNH)P(μ-N-t-Bu)2P+[(NH-t-Bu)(N-(CO 2R)-N-(CO2R)]. Treatment of ClP(μ-N-t-Bu) 2P[(N-t-Bu){N-(CO2-i-Pr)-N(H)(CO2-i-Pr)] (6) with 2,6-dicholorophenol affords (2,6-Cl2-C6H 3-O)P-(μ-N-t-Bu)2P+[(NH-t-Bu){N[(CO 2i-Pr)(HNCO2i-Pr)]}](Cl-)(2,6-Cl 2-C6H3-OH) (14) that has a structure similar to that of (CF3CH2O)P(μ-N-t-Bu)2P +[(NH-t-Bu){N[(CO2i-Pr)(HNCO2i-Pr)]}](Cl -) (13), but with an additional hydrogen bonded phenol. Both of these have the protonated betaine structure analogous to that of Ph3P +N(CO2R)NH(CO2R)(R′CO2) - (2) proposed in the Mitsunobu esterification. Two other compounds, (ArO)P(μ-N-t-Bu)2P+(NH-t-Bu){N(CO2i-Pr) (HNCO2i-Pr)}(Cl-) [Ar = 2,6-Me2C 6H3O- (15) and 2-Me-6-t-Bu-C6H3-O- (16)], are also prepared by the same route. Although NMR tube reactions of 11 or 12 with tetrachlorocatechol, catechol, 2,2′-biphenol, and phenol revealed significant changes in the 31P NMR spectra, attempted isolation of these products was not successful. On the basis of 31P NMR spectra, the phosphonium salt structure (t-BuNH)P(μ-N-t-Bu)2P +[(HN-t-Bu){N-(CO2R)-N(H)(CO2R)]-(ArO -) is proposed for these. The weakly acidic propan-2-ol or water did not react with 11 or 12, Treatment of 12 with carboxylic acids/p-toluenesulfonic acid gave the products (t-BuNH)P(μ-N-t-Bu)2P+[(HN-t- Bu){N-(CO2-i-Pr)-N(H)(CO2-i-Pr)](ArCO2-) [Ar = Ph (18), 4-Cl-C6H4CH2 (19), 4-Br-C 6H4 (20), 4-NO2-C6H4 (21)] and (t-BuNH)P(μ-N-t-Bu)2P+|(HN-t-Bu){N-(CO 2-i-Pr)-N(H)(CO2-i-Pr)](4-CH3-C 6H4SO3-) (22) that have essentially the same structure as 2. Compound 18 has additional stabilization by hydrogen bonding, as revealed by X-ray structure determination. Finally it is shown that the in situ generated (t-BuNH)P(μ-N-t-Bu)2P+[(HN-t-Bu) {N-(CO2Et)-N(H)(CO2Et)](4-NO2-C 6H4CO2-) can also effect Mitsunobu esterification. A comparison of the Ph3P-DIAD system with the analogous synthetically useful Ph3P-dimethyl acetylenedicarboxylate (DMAD) system is made.
The polyhedral nature of selenium-catalysed reactions: Se(iv) species instead of Se(vi) species make the difference in the on water selenium-mediated oxidation of arylamines
Capperucci, Antonella,Dalia, Camilla,Tanini, Damiano
supporting information, p. 5680 - 5686 (2021/08/16)
Selenium-catalysed oxidations are highly sought after in organic synthesis and biology. Herein, we report our studies on the on water selenium mediated oxidation of anilines. In the presence of diphenyl diselenide or benzeneseleninic acid, anilines react with hydrogen peroxide, providing direct and selective access to nitroarenes. On the other hand, the use of selenium dioxide or sodium selenite leads to azoxyarenes. Careful mechanistic analysis and 77Se NMR studies revealed that only Se(iv) species, such as benzeneperoxyseleninic acid, are the active oxidants involved in the catalytic cycle operating in water and leading to nitroarenes. While other selenium-catalysed oxidations occurring in organic solvents have been recently demonstrated to proceed through Se(vi) key intermediates, the on water oxidation of anilines to nitroarenes does not. These findings shed new light on the multifaceted nature of organoselenium-catalysed transformations and open new directions to exploit selenium-based catalysis.
Ni-NiO heterojunctions: a versatile nanocatalyst for regioselective halogenation and oxidative esterification of aromatics
Bhardwaj, Nivedita,Goel, Bharat,Indra, Arindam,Jain, Shreyans K.,Singh, Ajit Kumar,Tripathi, Nancy
, p. 14177 - 14183 (2021/08/16)
Herein, we report a facile method for the synthesis of Ni-NiO heterojunction nanoparticles, which we utilized for the nuclear halogenation reaction of phenol and substituted phenols usingN-bromosuccinimide (NBS). A remarkablepara-selectivity was achieved for the halogenated products under semi-aqueous conditions. Interestingly, blocking of thepara-position of phenol offeredortho-selective halogenation. In addition, the Ni-NiO nanoparticles catalyzed the oxidative esterification of carbonyl compounds with alcohol, diol or dithiol in the presence of a catalytic amount of NBS. It was observed that the aromatic carbonyls substituted with an electron-donating group favoured nuclear halogenation, whereas an electron-withdrawing group substitution in carbonyl compounds facilitated the oxidation reaction. In addition, the catalyst was magnetically separated and recycled 10 times. The tuned electronic structure at the Ni-NiO heterojunction controlled selectivity and activity as no suchpara-selectivity was observed with commercially available NiO or Ni nanoparticles.
