- Mild deprotection of the: N-tert -butyloxycarbonyl (N -Boc) group using oxalyl chloride
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We report a mild method for the selective deprotection of the N-Boc group from a structurally diverse set of compounds, encompassing aliphatic, aromatic, and heterocyclic substrates by using oxalyl chloride in methanol. The reactions take place under room temperature conditions for 1-4 h with yields up to 90percent. This mild procedure was applied to a hybrid, medicinally active compound FC1, which is a novel dual inhibitor of IDO1 and DNA Pol gamma. A broader mechanism involving the electrophilic character of oxalyl chloride is postulated for this deprotection strategy. This journal is
- Awuah, Samuel G.,George, Nathaniel,Ofori, Samuel,Parkin, Sean
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p. 24017 - 24026
(2020/07/23)
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- Transposed Paternò-Büchi reaction
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A complementary strategy of utilizing nπ? excited state of alkene instead of nππ? excited state of the carbonyl chromophore in a "transposed Paternò-Büchi" reaction is evaluated with atropisomeric enamides as the model system. Based on photophysical inves
- Kumarasamy, Elango,Raghunathan, Ramya,Kandappa, Sunil Kumar,Sreenithya,Jockusch, Steffen,Sunoj, Raghavan B.,Sivaguru
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supporting information
p. 655 - 662
(2017/05/16)
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- Nonsolvent application of ionic liquids: Organo-catalysis by 1-alkyl-3-methylimidazolium cation based room-temperature ionic liquids for chemoselective N-tert-butyloxycarbonylation of amines and the influence of the C-2 hydrogen on catalytic efficiency
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1-Alkyl-3-methylimidazolium cation based ionic liquids efficiently catalyze N-tert-butyloxycarbonylation of amines with excellent chemoselectivity. The catalytic role of the ionic liquid is envisaged as "electrophilic activation" of di-tert-butyl dicarbonate (Boc2O) through bifurcated hydrogen bond formation with the C-2 hydrogen of the 1-alkyl-3-methylimidazolium cation and has been supported by a downfield shift of the imidazolium C-2 hydrogen of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf2]) from δ 8.39 to 8.66 in the presence of Boc2O in the 1H NMR and a drastic reduction of the catalytic efficiency with 1-butyl-2,3-dimethylimidazolium ionic liquids that are devoid of the C-2 hydrogen. The differential time required for reaction with aromatic and aliphatic amines has offered means for selective N-t-Boc formation during inter and intramolecular competitions. Preferential N-t-Boc formation with secondary aliphatic amine has been achieved in the presence of primary aliphatic amine. Comparison of the catalytic efficiency for N-t-Boc formation with a common substrate revealed that [bmim][NTf2] is superior to the reported Lewis acid catalysts.
- Sarkar, Anirban,Roy, Sudipta Raha,Parikh, Naisargee,Chakraborti, Asit K.
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experimental part
p. 7132 - 7140
(2011/10/08)
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- PEG-mediated facile protocol for N-Boc protection of amines
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We have reported an efficient and eco-friendly protocol for the protection of various structurally and electronically divergent aryl and aliphatic amines using (Boc)2O in the presence of PEG-400 at room temperature. The reaction gave excellent
- Siddaiah,Basha,Padma Rao,Viplava Prasad,Suryachendra Rao
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experimental part
p. 1127 - 1129
(2011/02/28)
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- Indium(III) halides as new and highly efficient catalysts for N-tert-butoxycarbonylation of amines
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Indium(III) bromide and chloride efficiently catalysed the N-tert-butoxycarbonylation of amines with (Boc)2O at room temperature and under solvent-free conditions. Various aromatic, heteroaromatic and aliphatic amines were converted to N-tert-butylcarbamates in excellent yields in short times. Chiral amines, esters of α-amino acids and β-amino alcohols afforded optically pure N-t-Boc derivatives in high yields. The reactions were chemoselective and no competitive side reactions such as isocyanate, urea, and N,N-di-t-Boc formation were observed. Chemoselective conversion to N-tert-butylcarbamates took place with amino alcohols without any formation of oxazolidinones. Georg Thieme Verlag Stuttgart.
- Chankeshwara, Sunay V.,Chakraborti, Asit K.
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p. 2784 - 2788
(2008/02/05)
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- Copper(II) tetrafluoroborate as a novel and highly efficient catalyst for N-tert-butoxycarbonylation of amines under solvent-free conditions at room temperature
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Commercially available copper(II) tetrafluoroborate hydrate was found to be a highly efficient catalyst for chemoselective N-tert-butoxycarbonylation of amines with di-tert-butyl dicarbonate under solvent-free conditions and at room temperature. Various aromatic amines were protected as their N-tert-butyl carbamates in high yields and in short times. No competitive side reactions such as isocyanate, urea, and N,N-di-t-Boc formation was observed. Chemoselective N-tert-butoxycarbonylation was achieved with substrates bearing OH and SH groups. Chiral α-amino acid esters afforded the corresponding N-t-Boc derivatives in excellent yields.
- Chankeshwara, Sunay V.,Chakraborti, Asit K.
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p. 1087 - 1091
(2007/10/03)
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- HClO4-SiO2 as a new, highly efficient, inexpensive and reusable catalyst for N-tert-butoxycarbonylation of amines
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Perchloric acid adsorbed on silica-gel (HClO4-SiO2) was found to be a new, highly efficient, inexpensive and reusable catalyst for chemoselective N-tert-butoxycarbonylation of amines at room temperature and under solvent-free conditions. The Royal Society of Chemistry 2006.
- Chakraborti, Asit K.,Chankeshwara, Sunay V.
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p. 2769 - 2771
(2008/03/28)
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- Catalyst-free chemoselective N-tert-butyloxycarbonylation of amines in water
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Catalyst-free N-tert-butyloxycarbonylation of amines in water is reported. The N-t-Boc derivatives were formed chemoselectively without any isocyanate, urea, N,N-di-t-Boc, and O/S-t-Boc as side products. Chiral amines, esters of α-amino acids, and β-amino alcohol afforded optically pure N-t-Boc derivatives. Amino alcohol and 2-aminophenol afforded the N-t-Boc derivative without oxazolidinone formation. Selectivity was observed during competition of aromatic amine vs aliphatic amine, amine vs amino acid ester, amine vs amino alcohol, and primary amine vs secondary amine.
- Chankeshwara, Sunay V.,Chakraborti, Asit K.
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p. 3259 - 3262
(2007/10/03)
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- Recyclable chiral metathesis catalysts
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The present invention relates to chiral metal catalysts for stereoselective olefin metathesis reactions, which are recyclable and reusable in such metathesis reactions. The chiral metal-based metathesis catalysts of the invention comprise multidentate optically active or racemic chiral ligands that enable their use in asymmetric synthetic processes, such as for example, in ring-opening and ring-closing metathesis reactions (ROM and RCM, respectively) of alkenes. The catalysts of the invention are organometallic complexes of multivalent metals comprising one or more chiral bidentate ligands that exhibit superior reactivity and stereoselectivity properties. The present invention also provides methods of making such catalysts and methods for utilizing them in catalyzing stereoselective olefin metathesis reactions to provide asymmetric products in relatively high enantiomeric or stereoisomeric excess.
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- A Lewis acid-mediated protocol for the protection of aryl amines as their Boc-derivatives
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A new protocol of protection of poorly reactive aryl amines and functionalized amines with Boc2O in the presence of Zn(ClO 4)2·6H2O as the catalyst is reported. The catalytic action of Zn(ClO4)2·6H2O is specific for the activation of the pyrocarbonates, thus acid sensitive functionalities and stereochemical configurations of the starting materials remain unaltered in the protection process.
- Bartoli, Giuseppe,Bosco, Marcella,Locatelli, Manuela,Marcantoni, Enrico,Massaccesi, Massimo,Melchiorre, Paolo,Sambri, Letizia
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p. 1794 - 1798
(2007/10/03)
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- A recyclable chiral RU catalyst for enantioselective olefin metathesis. Efficient catalytic asymmetric ring-opening/cross metathesis in air
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The synthesis and structure of a new chiral bidentate imidazolinylidene ligand and a derived chiral Ru-based carbene are disclosed. The Ru complex is stereogenic at the metal center; it can be prepared in >98% diastereoselectivity and purified by silica gel chromatography with undistilled solvents. The air-stable Ru complex efficiently catalyzes ring-closing and ring-opening metathesis and is recyclable. The chiral complex is highly effective (0.5-10 mol % loading) in promoting enantioselective ring-opening/cross metathesis reactions (up to >98% ee). These enantioselective transformations can be effected in air, with unpurified solvent and with substrates that would only polymerize with Mo-based catalysts. Copyright
- Van Veldhuizen, Joshua J.,Garber, Steven B.,Kingsbury, Jason S.,Hoveyda, Amir H.
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p. 4954 - 4955
(2007/10/03)
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- Di-tert-butyl dicarbonate and 4-(dimethylamino)pyridine revisited. Their reactions with amines and alcohols
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The reaction of BOC2O in the presence and absence of DMAP was examined with some amines, alcohols, diols, amino alcohols, and aminothiols. Often, unusual products were observed depending on the ratio of reagents, reaction time, polarity of solvent, pK(a) of alcohols, or type of amine (primary or secondary). In reactions of aliphatic alcohols with BOC2O/DMAP, we isolated for the first time carbonic-carbonic anhydride intermediates; this helps explain the formation of symmetrical carbonates in addition to the O-BOC products. In the case of secondary amines, we succeeded to isolate unstable carbamic-carbonic anhydride intermediates that in the presence of DMAP led to the final N-BOC product. The effect of N-methylimidazole in place of DMAP was also examined.
- Basel, Yochai,Hassner, Alfred
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p. 6368 - 6380
(2007/10/03)
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- Isocyanates - Part 3. Synthesis of carbamates by DMAP-catalyzed reaction of amines with di-tert-butyldicarbonate and alcohols
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Carbamates are prepared by DMAP-catalyzed reaction of amines with di-tert-butyldicarbonate and subsequent trapping of the intermediate isocyanates with alcohols.
- Knoelker, Hans-Joachim,Braxmeier, Tobias
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p. 5861 - 5864
(2007/10/03)
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