- Sustainable Route Toward N-Boc Amines: AuCl3/CuI-Catalyzed N-tert-butyloxycarbonylation of Amines at Room Temperature
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N-tert-butoxycarbonyl (N-Boc) amines are useful intermediates in synthetic/medicinal chemistry. Traditionally, they are prepared via an indirect phosgene route with poor atom economy. Herein, a step- and atom-economic synthesis of N-Boc amines from amines, t-butanol, and CO was reported at room temperature. Notably, this N-tert-butyloxycarbonylation procedure utilized ready-made substrates, commercially available AuCl3/CuI as catalysts, and O2 from air as the sole oxidant. This catalytic system provided unique selectivity for N-Boc amines in good yields. More significantly, gram-scale preparation of medicinally important N-Boc amine intermediates was successfully implement, which demonstrated a potential application prospect in industrial syntheses. Furthermore, this approach also showed good compatibility with tertiary and other useful alcohols. Investigations of the mechanisms revealed that gold catalyzed the reaction and copper acted as electron transfer mediator in the catalytic cycle.
- Cao, Yanwei,Huang, Yang,He, Lin
-
-
- Nanoceria as an efficient and green catalyst for the chemoselective N-tert-butyloxycarbonylation of amines under the solvent-free conditions
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Nanocerium oxide mediated an efficient and green protocol has been described for the chemoselective N-tert-butyloxycarbonylation of amines under the solvent-free conditions at ambient temperature. Various aliphatic, aromatic and heteroaromatic amines were protected using developed protocol and several functional groups such as alcohol, phenol and ester were well tolerated under these conditions. The rapid reaction rate, mild conditions, very good functional group tolerance, excellent yield, solvent-free, easy recovery products and excellent catalyst recyclability are the advantages of this protocol. This makes the protocol feasible, economical and environmentally benign.
- Garad, Dnyaneshwar N.,Ingale, Ajit P.,Shinde, Sandeep V.,Ukale, Dattatraya
-
supporting information
p. 1656 - 1668
(2021/04/05)
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- Ultrasound promoted environmentally benign, highly efficient, and chemoselective N-tert-butyloxycarbonylation of amines by reusable sulfated polyborate
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The sulfated polyborate catalyzed an efficient and chemoselective N-tert-butyloxycarbonylation of amines under ultrasonic irradiation is developed. A broad substrate scope has been demonstrated for N-Boc protection of various primary/secondary amines. It allows converting several aliphatic/aryl/heteroaryl amines, amino alcohol, aminoester, and chiral amines to their N-Boc-protected derivatives under solvent-free conditions with excellent yields. The protocol has several advantages such as easy catalyst, and product isolation, short reaction time, excellent yields, outstanding chemoselectivity, and catalyst recyclability, among others. This makes the process practicable, economical, and environmentally benign.
- Pise, Ashok S.,Ingale, Ajit P.,Dalvi, Navnath R.
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supporting information
p. 3768 - 3780
(2021/10/26)
-
- Thiamine hydrochloride as a recyclable organocatalyst for the efficient and chemoselective N-tert-butyloxycarbonylation of amines
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Thiamin hydrochloride promoted highly efficient and ecofriendly approach has been described for the chemoselective N-tert-butyloxycarbonylation of amines under solvent-free conditions at ambient temperature. The demonstrated approach has been applicable for the N-Boc protection of variety of aliphatic, aryl, heteroaryl amines. The chemoselective protection of amino group occurs in chiral amines and amino alcohol without racemization in high yield. Thiamin hydrochloride is stable, economical, easy to handle and environmentally friendly.
- Ingale, Ajit P.,Garad, Dnyaneshwar N.,Ukale, Dattatraya,Thorat, Nitin M.,Shinde, Sandeep V.
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supporting information
p. 3791 - 3804
(2021/11/04)
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- Sulfated tungstate: A highly efficient, recyclable and ecofriendly catalyst for chemoselective N-tert butyloxycarbonylation of amines under the solvent-free conditions
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Sulfated tungstate catalyzed an efficient and ecofriendly protocol has been described for the chemoselective N-tert-butyloxycarbonylation of amines under the solvent-free conditions at room temperature. The variety of functionalized aliphatic, aromatic and heteroaromatic amines efficiently undergoes the N-tert-butyloxycarbonylation under the developed protocol. The aminoalcohol, aminophenol, aminoester as well as various chiral amines underwent the chemoselective N-Boc protection under the optimized reaction condition. The rapid reaction rate, mild conditions, very good functional group tolerance, excellent yield, solvent-free, easy recovery products and excellent catalyst recyclability are the advantages of this protocol. This makes the protocol feasible, economical and environmentally benign.
- Ingale, Ajit P.,Shinde, Sandeep V.,Thorat, Nitin M.
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supporting information
p. 2528 - 2543
(2021/07/02)
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- A Greener Approach for the Chemoselective Boc Protection of Amines Using Sulfonated Reduced Graphene Oxide as a Catalyst in Metal- And Solvent-Free Conditions
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Sulfonated reduced graphene oxide (SrGO) has displayed great potential as a solid acid catalyst due to its efficiency, cost-effectiveness, and reliability. In this study, SrGO was synthesized by the introduction of sulfonic acid-containing aryl radicals onto chemically reduced graphene oxide using ultrasonication. The SrGO catalyst was characterized by Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Further, SrGO was effectively utilized as a metal-free and reusable solid acid catalyst for the chemoselective N - t -Boc protection of various aromatic and aliphatic amines under solvent-free conditions. The N - t -Boc protection of amines was easily achieved under ambient conditions affording high yields (84-95percent) in very short reaction times (5 min-2 h). The authenticity of the approach was confirmed by a crystal structure. The catalyst could be easily recovered and was reused up to seven consecutive catalytic cycles without any substantial loss in its activity.
- Awasthi, Satish K.,Mishra, Anupam,Mittal, Rupali
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p. 591 - 601
(2020/02/13)
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- Synthesis of Amide Enol Carbamates and Carbonates through Cu(OTf)2-Catalyzed Reactions of Ynamides with t-Butyl Carbamates/Carbonates
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A highly regioselective approach to access amide enol carbamates and carbonates 5a-5c′, 7a-7h, and 9 was developed through Cu(OTf)2-catalyzed reactions of ynamides 4 with t-butyl carbamates 2 and 8 and t-butyl carbonates 6. Moreover, this strategy was successfully applied to generate amide enol carbamates 11a-11s and 14a-14f from imides 10 and 13 with ynamides through an N-Boc cleavage-addition ring-opening process. A range of substituents was amenable to this transformation, and the desired amide enol carbamates and carbonates were obtained in moderate to good yields.
- Han, Pan,Mao, Zhuo-Ya,Li, Ming,Si, Chang-Mei,Wei, Bang-Guo,Lin, Guo-Qiang
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p. 4740 - 4752
(2020/04/30)
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- Amine-Responsive Disassembly of AuI–CuI Double Salts for Oxidative Carbonylation
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A sensitive amine-responsive disassembly of self-assembled AuI-CuI double salts was observed and its utilization for the synergistic catalysis was enlightened. Investigation of the disassembly of [Au(NHC)2][CuI2] revealed the contribution of Cu-assisted ligand exchange of N-heterocyclic carbene (NHC) by amine in [Au(NHC)2]+ and the capacity of [CuI2]? on the oxidative step. By integrating the implicative information coded in the responsive behavior and inherent catalytic functions of d10 metal complexes, a catalyst for the oxidative carbonylation of amines was developed. The advantages of this method were clearly reflected on mild reaction conditions and the significantly expanded scope (51 examples); both primary and steric secondary amines can be employed as substrates. The cooperative reactivity from Au and Cu centers, as an indispensable prerequisite for the excellent catalytic performance, was validated in the synthesis of (un)symmetric ureas and carbamates.
- Cao, Yanwei,Yang, Jian-Gong,Deng, Yi,Wang, Shengchun,Liu, Qi,Shen, Chaoren,Lu, Wei,Che, Chi-Ming,Chen, Yong,He, Lin
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supporting information
p. 2080 - 2084
(2019/12/24)
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- Dual Benzophenone/Copper-Photocatalyzed Giese-Type Alkylation of C(sp3)?H Bonds
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Photocatalyzed Giese-type alkylations of C(sp3)?H bonds are very attractive reactions in the context of atom-economy in C?C bond formation. The main limitation of such reactions is that when using highly polymerizable olefin acceptors, such as unsubstituted acrylates, acrylonitrile, or methyl vinyl ketone, radical polymerization often becomes the dominant or exclusive reaction pathway. Herein, we report that the polymerization of such olefins is strongly limited or suppressed when combining the photocatalytic activity of benzophenone (BP) with a catalytic amount of Cu(OAc)2. Under mild and operationally simple conditions, the Giese adducts resulting from the C(sp3)?H functionalization of amines, alcohols, ethers, and cycloalkanes could be synthesized. Preliminary mechanistic studies have revealed that the reaction does not proceed through a radical chain, but through a dual BP/Cu photocatalytic process, in which both CuII and low-valent CuI/0 species, generated in situ by reduction by the BP ketyl radical, may react with α-keto or α-cyano intermediate radicals, thus preventing polymerization.
- Abadie, Baptiste,Jardel, Damien,Pozzi, Gianluca,Toullec, Patrick,Vincent, Jean-Marc
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supporting information
p. 16120 - 16127
(2019/11/26)
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- Chemoselective: N-tert -butyloxycarbonylation of amines in glycerol
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A catalyst-free, efficient and green protocol has been developed for the chemoselective N-Boc protection of amines by using glycerol as a solvent at room temperature. A variety of functionalized amines, such as aliphatic, aromatic as well as heteroaromatic were protected using the developed protocol. N-tert-Butyloxycarbonylation derivatives were formed without the formation of isocyanate, urea, N,N-di-t-Boc, or oxazolidinone as side products. The operational simplicity, cleaner reaction, rapid reaction convergence, functional group tolerance, excellent yield, high selectivity, catalyst-free feature and solvent recyclability are the distinct advantages of this protocol. Owing to these merits, this protocol is feasible, economical and environmentally benign.
- Ingale, Ajit P.,More, Vishal K.,Gangarde, Uddhav S.,Shinde, Sandeep V.
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supporting information
p. 10142 - 10147
(2018/06/18)
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- C(sp3)?H Cyanation Promoted by Visible-Light Photoredox/Phosphate Hybrid Catalysis
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Inspired by the reaction mechanism of photo-induced DNA cleavage in nature, a C(sp3)?H cyanation reaction promoted by visible-light photoredox/phosphate hybrid catalysis was developed. Phosphate radicals, generated by one-electron photooxidation of phosphate salt, functioned as a hydrogen-atom-transfer catalyst to produce nucleophilic carbon radicals from C(sp3)?H bonds with a high bond-dissociation energy. The resulting carbon radicals were trapped by a cyano radical source (TsCN) to produce the C?H cyanation products. Due to the high functional-group tolerance and versatility of the cyano group, the reaction will be useful for realizing streamlined building block syntheses and late-stage functionalization of drug-like molecules.
- Wakaki, Takayuki,Sakai, Kentaro,Enomoto, Takafumi,Kondo, Mio,Masaoka, Shigeyuki,Oisaki, Kounosuke,Kanai, Motomu
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supporting information
p. 8051 - 8055
(2018/06/15)
-
- Photoredox-Mediated Direct Cross-Dehydrogenative Coupling of Heteroarenes and Amines
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A photoredox-mediated direct cross-dehydrogenative coupling reaction to accomplish α-aminoalkylation of N-heteroarenes is reported. This mild reaction has a broad substrate scope, offers the first general method for synthesis of aminoalkylated N-heteroarenes without the need for substrate prefunctionalization, and is scalable to the gram level. Furthermore, the reaction was found to be applicable to other hydrogen donors besides amines (i.e., ethers, an aldehyde, a formamide, p-xylene, and alkanes), thus enabling the preparation of N-heteroarenes bearing various types of substituents.
- Dong, Jianyang,Xia, Qing,Lv, Xueli,Yan, Changcun,Song, Hongjian,Liu, Yuxiu,Wang, Qingmin
-
supporting information
p. 5661 - 5665
(2018/09/21)
-
- [TPA][Pro] ionic liquid as efficient reaction medium for N-tert-Boc protection of amines
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A facile and efficient N-tert-Boc protection of amines is described by the reaction of various primary, secondary, benzylic and aryl amines with di-tert-butyl dicarbonate in the ionic liquid [TPA][Pro] at room temperature. All the N-tert-butylcarbamates are afforded in excellent yields. A catalyst-free method was developed and the ionic liquid [TPA][Pro] can be recovered and reused for several times without loss of its activity.
- Vijaya Durga,Rambabu,Srinivasa Reddy,Hari Babu
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p. 1313 - 1316
(2017/05/02)
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- Copper nanoparticles catalyzed N-H functionalization: An efficient solvent-free N-tert-butyloxycarbonylation strategy
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A chemoselective transformation of amines to their tert-butyloxycarbonyl (Boc) protected derivatives (NBoc) is described using Cu-NPs under solvent-free conditions. Simple method, rapid reaction rate, mild conditions, tolerance of a wide range of functional groups, excellent yield, ease recovery and high catalytic turnover are the salient features of this approach. tert-Butyloxycarbonylation of chiral amino acid esters and amino alcohols were performed without racemization.
- Deb, Barnali,Debnath, Sudipto,Deb, Anindita,Maiti, Dilip K.,Majumdar, Swapan
-
supporting information
p. 629 - 633
(2017/01/25)
-
- Heterobimetallic dinuclear lanthanide alkoxide complexes as acid-base bifunctional catalysts for synthesis of carbamates under solvent-free conditions
-
Heterobimetallic dinuclear lanthanide alkoxide complexes Ln2Na8(OCH2CH2NMe2)12(OH)2 [Ln: I (Nd), II (Sm), III (Yb) and IV (Y)] were used as efficient acid-base bifunctional catalysts for the synthesis of carbamates from dialkyl carbonates and amines as well as the N-Boc protection of amines. The cooperative catalysts showed high catalytic activity and a wide scope of substrates with good to excellent yields under solvent-free conditions. The systems have shown higher catalytic activities due to the noteworthy synergistic interactions of Lewis acid center-Br?nsted basic center. The comparison of catalytic efficiency between mono- and dinuclear heterobimetallic lanthanide alkoxide analogues was also investigated.
- Zeng, Ruijie,Bao, Linquan,Sheng, Hongting,Sun, Lili,Chen, Man,Feng, Yan,Zhu, Manzhou
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p. 78576 - 78584
(2016/09/09)
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- Efficient N-Boc protection of amines by a reusable heterogeneous solid acid nanocatalyst at room temperature
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An efficient and rapid protocol for chemoselective N-Boc protection of various structurally different aryl, aliphatic, and heterocyclic amines is reported with (Boc)2O using mesoporous silica phenylsulfonic acid (SBA-15-Ph-SO3H) as a recyclable and heterogeneous solid acid nanocatalyst under solvent-free condition at ambient temperature. The catalyst can be easily recovered and reused for ten reaction cycles for protection of amines without considerable loss of activity. The advantages of this green method are simplicity, easy workup, chemoselectivity, short reaction time, and excellent yield.
- Veisi, Hojat,Sedrpoushan, Alireza,Ghazizadeh, Habibollah,Hemmati, Saba
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p. 1451 - 1461
(2016/04/26)
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- CHEMICAL BLOWING AGENT AND THERMALLY EXPANDABLE THERMOPLASTIC COMPOSITION
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The present invention relates to a chemical blowing agent comprising at least one tertiary alkyl carbamate. The chemical blowing agent can be activated thermally and is suitable for foaming thermoplastic materials and can for example be incorporated into thermally expandable baffle and/or reinforcement elements which are used in automotive manufacturing and building insulation.
- -
-
Page/Page column 27; 28; 29
(2016/07/05)
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- General solvent-free highly selective N-tert-butyloxycarbonylation strategy using protic ionic liquid as an efficient catalyst
-
A simple, rapid and solvent-free protocol is described for the chemo-selective transformation of amines to tert-butyloxycarbonyl protected derivatives (NHBoc) using Boc2O and imidazolium trifluoroacetate protic ionic liquid (5-20 mol%). Unwanted side products such as isocyanate, urea or N,N-di-Boc were not detected. The scope of the protection strategy was successfully explored for substrate alcohols, phenols and thiol at elevated temperatures. Optically pure amino acids, amino acid esters and amino alcohols were efficiently converted to the corresponding N-Boc protected derivatives in excellent yields without racemization at the chiral center. The distinct advantages of this method are: operational simplicity, cleaner reaction, high selectivity, excellent yield, rapid reaction convergence, easy preparation and recyclability of the catalyst.
- Majumdar, Swapan,De, Jhinuk,Chakraborty, Ankita,Maiti, Dilip K.
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p. 24544 - 24550
(2014/07/07)
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- Solvent free N-Boc protection of amines using amberlystr a 21 solid base resin as a reusable heterogeneous catalyst
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An efficient, environmentally benign, highly facile and convenient synthetic protocol for the selective t-butyl carboxylation of aliphatic, aromatic and heterocyclic amines using AmberlystR A 21 catalyst; a mild basic solid resin under solvent free conditions is reported. This method explores several advantages such as reusability of the heterogeneous catalyst, cleaner reaction profile, mild and solvent free system, short reaction time, operational simplicity, high conversions , excellent product yields and low cost of the catalyst. Furthermore since the catalyst is mild basic, decomposition of the carbamate formed is not observed if the reaction is continued for prolonged time as in the case of Lewis acid catalyzed N-Boc protection. This makes the present protocol a useful and attractive for N-Boc protection of amines.
- Tekale, Sunil U.,Kauthale, Sushama S.,Pawar, Rajendra P.
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p. 1619 - 1623
(2013/09/12)
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- A mild and green method for the N-BOC protection of amines without assistant of catalyst under solvent-free conditions
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A facile, green and versatile method for the Boc protection of amines has been developed by a treatment with (Boc)2O without any additive at room temperature. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic), aromatic, and heteroaromatic amines; primary and secondary amines. The advantages of this method are green, simplicity, short reaction times and excellent yields.
- Mojtahedi, Mohammad Majid,Niknejad, Nina,Veisi, Hojat
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p. 121 - 125
(2013/07/26)
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- Iron(III)triflate as a highly efficient, recyclable and green catalyst for the N-Boc protection of amines
-
Iron (III) triflate was used as an efficient catalyst for N-t-butoxycarbonylation of amines with di-t-butyl dicarbonate under solvent-free conditions at room temperature. Various aliphatic, aromatic, heterocyclic amines and aminols were protected as their corresponding mono-carbamates in excellent yields and short reaction times. Only two of the 23 monocarbamates were new. No competitive side reactions such as isocyanate, urea, nor N,N-di-Boc formation were observed. The reported method is mild and has the advantages of low cost, chemoselectivity and, because no solvent is used and the catalyst can be recycled, it is classifiable as a green procedure.
- Feng, Chengliang,Chu, Ningning,Zhang, Shuguang,Cai, Jin,Chen, Junqing,Hu, Huayou,Ji, Min
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p. 757 - 760
(2014/01/23)
-
- Aminolysis of benzyl 2-pyridyl thionocarbonate and t-butyl 2-pyridyl thionocarbonate: Effects of nonleaving groups on reactivity and reaction mechanism
-
A kinetic study is reported for nucleophilic substitution reactions of benzyl 2-pyridyl thionocarbonate (5b) and t-butyl 2-pyridyl thionocarbonate (6b) with a series of alicyclic secondary amines in H2O at 25.0 °C. Generalbase catalysis, which has often been reported to occur for aminolysis of esters possessing a C=S electrophilic center, is absent for the reactions of 5b and 6b. The Bronsted-type plots for the reactions of 5b and 6b are linear with ssnuc = 0.29 and 0.43, respectively, indicating that the reactions of 5b proceed through a stepwise mechanism with formation of a zwitterionic tetrahedral intermediate (T±) being the rate-determining step while those of 6b proceed through a concerted mechanism. The reactivity of 5b and 6b is similar to that of their oxygen analogues (i.e., benzyl 2-pyridyl carbonate 5a and t-butyl 2-pyridyl carbonate 6a, respectively), indicating that the effect of modification of the electrophilic center from C=O to C=S (i.e., from 5a to 5b and from 6a to 6b) on reactivity is insignificant. In contrast, 6b is much less reactive than 5b, indicating that the replacement of the PhCH2 in 5b by the t-Bu in 6b results in a significant decrease in reactivity as well as a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway). It has been concluded that the contrasting reactivity and reaction mechanism for the reactions of 5b and 6b are not due to the electronic effects of PhCH2 and t-Bu but are caused by the large steric hindrance exerted by the bulky t-Bu in 6b.
- Kim, Min-Young,Lee, Jae-In,Um, Ik-Hwan
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p. 1115 - 1119
(2013/07/28)
-
- A kinetic study on aminolysis of t-butyl 4-pyridyl carbonate and related compounds: Effect of leaving and nonleaving groups on reaction mechanism
-
Second-order rate constants kN have been measured spectrophotometrically for nucleophilic substitution reactions of t-butyl 4-pyridyl carbonate 8 with a series of alicyclic secondary amines in H 2O at 25.0 ± 0.1 °C. The Bronsted-type plot for the reactions of 8 is linear with βnuc = 0.84. The βnuc value obtained for the reactions of 8 is much larger than that reported for the corresponding reactions of t-butyl 2-pyridyl carbonate 6 (i.e., βnuc = 0.44), which was proposed to proceed through a forced concerted mechanism. Thus, the aminolysis of 8 has been concluded to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate T±, in which expulsion of the leaving-group from T± occurs at the rate-determining step (RDS). In contrast, aminolysis of benzyl 4-pyridyl carbonate 7 has been reported to proceed through two intermediates, T± and its deprotonated form T- on the basis of the fact that the plots of pseudo-first-order rate constant kobsd vs. amine concentration curve upward. The current study has demonstrated convincingly that the nature of the leaving and nonleaving groups governs the reaction mechanism. The contrasting reaction mechanisms have been rationalized in terms of an intramolecular H-bonding interaction, steric acceleration, and steric inhibition.
- Kang, Ji-Sun,Lee, Jae-In,Um, Ik-Hwan
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p. 2971 - 2975
(2012/10/29)
-
- Simple and efficient method for n-boc protection of amines using PEG-400 as a reaction medium under mild conditions
-
Simple and efficient method for N-Boc protection of amines using PEG-400 as an ecofriendly reaction medium at room temperature is described. Various aromatic, heteroaromatic, and aliphatic amines were converted to the corresponding N-tert-butyl-carbamates in good to excellent yields in short times.
- Zeng, Hongyao,Li, Yongjia,Shao, Huawu
-
experimental part
p. 25 - 32
(2011/10/19)
-
- Magnetic nanoparticles catalyzed N-tert-butoxycarbonylation of Amines and amine derivatives
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A simple and efficient protocol for the chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butyl dicarbonate using magnetically recoverable γ-Fe2O3@SiO 2 nanoparticles is reported. The catalyst can be easily recovered and recycled without a significant loss in the catalytic activity. No competitive side reactions, such as formation of isocyanate, urea, oxazolidinone, and N,N-di-Boc derivatives were obsereved.
- Akbari, Jafar,Sajirani, Soghra B.,Nezhad, Jafar M.,Heydari, Akbar
-
experimental part
p. 165 - 168
(2012/07/14)
-
- Microwave assisted mild, rapid, solvent-less, and catalyst-free chemoselective N-tert-butyloxycarbonylation of amines
-
Microwave assisted simple, rapid, solventless, and catalyst-free chemoselective method for the protection of amino group in aromatic, aliphatic, heterocyclic, aralkyl amines, phenyl hydrazine, and amino acid esters in good to excellent isolated yield (83-98%) in short reaction time (2-12 min) has been reported.
- Dighe, Satish N.,Jadhav, Hemant R.
-
p. 5803 - 5806
(2012/10/29)
-
- Zinc chloride promoted efficient and facile BOC protection of amines
-
Amines are efficiently protected as their BOC derivatives under mild reaction conditions when reacted with BOC anhydride in presence of ZnCl2. The present method is applicable to a variety of amines including aliphatic, aromatic as well as heteroaromatic amines. This protocol appears to be competitive and in some cases superior to previously reported procedures that work under basic conditions.
- Arifuddin, M.,Lakshmikant, N.,Rajasekar, N.,Shinde, D. B.
-
p. 1168 - 1172,5
(2020/08/31)
-
- Kinetics and reaction mechanism of aminolyses of benzyl 2-pyridyl carbonate and t-butyl 2-pyridyl carbonate in acetonitrile
-
Second-order rate constants (kN) have been measured spectrophotometrically for the reactions of benzyl 2- pyridyl carbonate 3 and t-butyl 2-pyridyl carbonate 4 with a series of alicyclic secondary amines in MeCN at 25.0 ± 0.1 ° C. Substrate 4 is much less reactive than 3 and the steric hindrance exerted by the bulky t-Bu group in 4 has been attributed to its decreased reactivity. The Bronsted-type plots for the reactions of 3 and 4 are linear with ssnuc = 0.57 and 0.45, respectively. Thus, the reactions have been concluded to proceed through a concerted mechanism, although the current reactions were expected to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate T±. It has been proposed that the rate of leaving-group expulsion is accelerated by the intramolecular H-bonding interaction in T± and the "push" provided by the RO group through the resonance interaction. Thus, the enhanced nucleofugality forces the reactions to proceed through a concerted mechanism. The reactivity-selectivity principle (RSP) is not applicable to the current reaction systems, since the reaction of the less reactive 4 results in a smaller ssnuc than that of the more reactive 3. Steric hindrance exerted by the bulky t-Bu group in 4 has been suggested to be responsible for the failure of the RSP. Copyright
- Bae, Ae Ri,Um, Ik-Hwan
-
scheme or table
p. 1547 - 1550
(2012/07/28)
-
- Solvent free, N,N'-carbonyldiimidazole (CDI) mediated amidation
-
The method involves CDI mediated amidation under solvent-free conditions. The protocol is green, simple, and scalable and has broad structural applicability. The protocol has also been used for BOC protection of amine. The protocol has reduced the time for CDI mediated amidation from 2-4 h to 5-10 min without the use of any dry organic solvent and nitrogen atmosphere.
- Verma, Sanjeev K.,Ghorpade, Ramarao,Pratap, Ajay,Kaushik
-
experimental part
p. 2373 - 2376
(2012/05/31)
-
- Guanidine hydrochloride as an organocatalyst for N-Boc protection of amino groups
-
A simple and efficient method for the chemoselective N-Boc protection of the amine moiety in a variety of compounds is described using di-tert-butyl dicarbonate and guanidine hydrochloride as an organocatalyst in ethanol at 35-40°C. Selective mono-N-Boc protection of diamines and chemoselective protection of hydroxylamines without formation of any side products is achieved. Amino acids and peptides are N-Boc protected efficiently in excellent yields under convenient reaction conditions.
- Jahani, Fatemeh,Tajbakhsh, Mahmood,Golchoubian, Hamid,Khaksar, Samad
-
supporting information; experimental part
p. 1260 - 1264
(2011/04/15)
-
- An efficient and highly chemoselective N-Boc protection of amines, amino acids, and peptides under heterogeneous conditions
-
A simple and efficient procedure for chemoselective mono-N-Boc protection of various structurally diverse amines, amino acids, and peptides with di-tert-butyl dicarbonate using Amberlyst-15 as catalyst in ethanol is described. The catalyst can be readily separated from the reaction products with simple filtration and recovered for direct reuse. No competitive side-reactions such as formation of isocyanate, urea, oxazolidinone, and N,N-di-Boc derivatives were observed.
- Jahani, Fatemeh,Tajbakhsh, Mahmood,Khaksar, Samad,Azizi, Mohamad Reza
-
experimental part
p. 1035 - 1043
(2012/07/27)
-
- ZnO nanorods as an efficient and heterogeneous catalyst for N-Boc protection of amines and amine derivatives
-
An efficient ZnO nano catalyst, which was readily prepared from Zn(CH3CO2)2, 2H2O and PVP by a chemical solution approach has successfully catalyzed N-tertbutoxy carbonylation of amines. The ZnO nanorods were successful and gave promising results for highly active and chemoselective as well as easily recyclable catalyst for the NBoc protection reaction of a wide variety of amines. The catalyst could be easily recycled for five times without noticeable decrease in catalytic activity. The ZnO nanocatalyst was characterized with XRD and SEM.
- Nouria, Azita,Akbari, Jafar,Heydaric, Akbar,Nouri, Arezu
-
experimental part
p. 38 - 42
(2012/05/04)
-
- Ferric chloride-promoted efficient and facile BOC protection of amines
-
Amines are efficiently protected as their tertiary butyloxycarbonyl (BOC) derivatives under mild reaction condition when reacted with (BOC)2O in the presence of FeCl3. The present method is applicable to a variety of amines including aliphatic, aromatic, and hetero aromatic amines.
- Tasneem,Rajanna
-
experimental part
p. 715 - 719
(2011/04/12)
-
- Protic ionic liquid [TMG][Ac] as an efficient, homogeneous and recyclable catalyst for Boc protection of amines
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An efficient and practical protocol for the chemoselective N-Boc protection of various structurally different aryl, aliphatic and heterocyclic amines was carried out with (Boc)2O using protic 1, 1, 3, 3-tetra-methylguanidinium acetate (10 mol%) as recyclable catalyst under solvent free condition at ambient temperature. No competitive side reactions (isocyanate, urea and N, N-di-Boc) were observed. α-Amino alcohols afforded the N-Boc-derivative without oxazolidinone formation.
- Akbari, Jafar,Heydari, Akbar,Ma'mani, Leila,Hassan Hosseini, Seyed
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experimental part
p. 544 - 547
(2010/11/05)
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- An expeditious, efficient green methodology for the Boc protection of amines and silyl protection of alcohols over tungstophosphoric acid-doped mesoporous silica
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An efficient, chemoselective and eco-friendly protocol for the protection of amines as N-tert-butylcarbamate using (Boc)2O and protection of alcohols as silyl ether using HMDS over tungstophosphoric acid/SBA15 has been developed. Solventless condition, easy work-up, short reaction time, excellent yields and reusability of the catalyst are the striking features of this methodology which can be considered to be one of the better methods for the protection of amines and alcohols.
- Karmakar, Bikash,Banerji, Julie
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experimental part
p. 3855 - 3858
(2010/08/20)
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- Thioglycoluril as a highly efficient, recyclable and novel organocatalyst for N-Boc protection of amines
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A simple and efficient protocol for the chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butyl dicarbonate using thioglycoluril as the catalyst is described. The catalyst can be readily separated from the reaction products by simple filtration and recovered for reuse. No competitive side reactions, such as formation of isocyanate, urea, oxazolidinone, and N,N-di-Boc derivatives were observed.
- Khaksar, Samad,Vahdat, Seyed Mohammad,Tajbakhsh, Mahmood,Jahani, Fatemeh,Heydari, Akbar
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experimental part
p. 6388 - 6391
(2011/01/03)
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- Amberlyst-15: a mild, efficient and reusable heterogeneous catalyst for N-tert-butoxycarbonylation of amines
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A mild and versatile method has been developed for the chemoselective N-tert-butoxycarbonylation of amines in the presence of Amberlyst-15 under solvent-free condition. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic) and aromatic amines.
- Kumar, K. Shiva,Iqbal, Javed,Pal, Manojit
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experimental part
p. 6244 - 6246
(2010/01/11)
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- An efficient and chemoselective Br?nsted acidic ionic liquid-catalyzed N-Boc protection of amines
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The first report of a Br?nsted acidic ionic liquid, 1-methylimidazolium tetrafluoroborate [(HMIm)BF4], catalyzed efficient and chemoselective N-Boc protection of various amines using (Boc)2O is presented. Optically pure amino alcohols and amino acid esters were converted efficiently to their corresponding optically pure N-Boc derivatives. The reported method is mild, solvent-free and has the advantages of both homogeneous and heterogeneous catalysis with high product yields, selectivity and ease of product separation.
- Sunitha, Sadula,Kanjilal, Sanjit,Reddy, P. Srinivasa,Prasad, Rachapudi B.N.
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p. 2527 - 2532
(2008/09/19)
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- Hydrogen bond catalyzed chemoselective N-tert-butoxycarbonylation of amines
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A novel, chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butoxypyrocarbonate (Boc)2O is described that relies on selective carbonyl activation by hydrogen bond formation. This mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor.
- Khaksar, Samad,Heydari, Akbar,Tajbakhsh, Mahmood,Vahdat, Seyed Mohammad
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p. 3527 - 3529
(2008/09/21)
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- 1,1,1,3,3,3-Hexafluoroisopropanol: A recyclable organocatalyst for N-Boc protection of amines
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A simple and efficient protocol for the chemoselective mono-N-Boc protection of various structurally diverse amines with di-tert-butyl dicarbonate using 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as solvent and catalyst is described. The catalyst can be readily separated from the reaction products and recovered for direct reuse. No competitive side reactions such as formation of isocyanate, urea, and N,N-di-Boc were observed. α-Amino alcohols afforded the N-Boc derivatives without oxazolidinone formation. Georg Thieme Verlag Stuttgart.
- Heydari, Akbar,Khaksar, Samad,Tajbakhsh, Mahmood
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experimental part
p. 3126 - 3130
(2009/04/06)
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- Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst
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A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)2O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.
- Upadhyaya, Dharita J.,Barge, Alessandro,Stefania, Rachele,Cravotto, Giancarlo
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p. 8318 - 8322
(2008/04/13)
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- N-tert-Butoxycarbonylation of amines using H3PW12O40 as an efficient heterogeneous and recyclable catalyst
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The commercially available heteropoly acid H3PW12O40 (0.5 mol %) is a very efficient and environmentally benign catalyst for N-tert-butoxycarbonylation of amines (primary, secondary) with di-tert-butyl dicarbonate at room temperature in short reaction times (10 min). No competitive side products such as isocyanates, ureas, N,N-di-tert-butoxycarbonyls, O-Boc and oxazolidinones were observed. Chiral α-amino alcohols and esters afforded the corresponding N-Boc derivatives chemoselectively in excellent yields.
- Heydari, Akbar,Shiroodi, Roohollah Kazem,Hamadi, Hossein,Esfandyari, Maryam,Pourayoubi, Mehrdad
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p. 5865 - 5868
(2008/02/09)
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- Facile N-tert-butoxycarbonylation of amines using La(NO3)3·6H2O as a mild and efficient catalyst under solvent-free conditions
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Facile N-tert-butoxycarbonylation of amines is described by the treatment of various primary, secondary, benzylic and aryl amines with di-tert-butyl dicarbonate in the presence of catalytic amounts of La(NO3)3·6H2O under solvent-free conditions at room temperature to afford N-tert-butylcarbamates in excellent yields.
- Suryakiran,Prabhakar,Reddy, T. Srikanth,Rajesh,Venkateswarlu
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p. 8039 - 8042
(2007/10/03)
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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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- 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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- A highly chemoselective Boc protection of amines using sulfonic-acid-functionalized silica as an efficient heterogeneous recyclable catalyst
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A facile and versatile method for the chemoselective Boc protection of amines has been developed by a treatment with (Boc)2O in the presence of sulfonic-acid-functionalized silica as a catalyst. The method is general for the preparation of N-Boc derivatives of aliphatic (acyclic and cyclic), aromatic, and heteroaromatic amines; primary and secondary amines; aminols, amino-esters; and sulfonamides. The catalyst works under heterogeneous conditions and can be recycled.
- Das, Biswanath,Venkateswarlu, Katta,Krishnaiah, Maddeboina,Holla, Harish
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p. 7551 - 7556
(2008/02/08)
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- Molecular iodine-catalyzed facile procedure for N-Boc protection of amines
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An efficient and practical protocol for the protection of various structurally and electronically divergent aryl and aliphatic amines using (Boc)2O in the presence of a catalytic amount of molecular iodine (10 mol%) under solvent-free conditions at ambient temperature is presented.
- Varala, Ravi,Nuvula, Sreelatha,Adapa, Srinivas R.
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p. 8283 - 8286
(2007/10/03)
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- N-boc protection of amines with di-tert-butyldicarbonate in water under neutral conditions in the presence of β-cyclodextrin
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A new protocol for protection of aryl and aliphatic amines was developed with (Boc)2O in the presence of β-cyclodextrin in water. A catalytic amount of β-cyclodextrin is specific for activation of amines. This procedure works well on a wide variety of both electron-rich and electron-deficient amines. Georg Thieme Verlag Stuttgart.
- Somi Reddy,Narender,Nageswar,Rama Rao
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p. 1110 - 1112
(2007/10/03)
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- Lithium perchlorate-catalyzed Boc protection of amines and amine derivatives
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A new mild and chemoselective method for mono-N-protection of amines and amine derivatives as tert-butoxycarbonyl derivatives is reported. The reaction proceeds with lithium perchlorate (20 mol %) and pyrocarbonates, and shows general applicability. The catalytic action of LiClO4 is specific for the activation of Boc2O, thus acid-sensitive functionalities of the starting materials remain unchanged in the protection process. This procedure works well for sterically hindered primary amine as well as electron-deficient primary arylamines, primary and secondary amino alcohols, α-amino acid esters, hydroxylamines, hydrazines and sulfonamides.
- Heydari, Akbar,Hosseini, Seyed Esmaeil
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p. 1929 - 1932
(2007/10/03)
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- Reactions on a Solid Surface. A Simple, Economical, and Efficient Acylation of Alcohols, Amines over Al2O3
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Al2O3 brings about a rapid acylation of a range of alcohols and amines with acid chlorides and acid anhydrides, respectively. Amines are easily Boc- and Cbz-protected on reaction with Boc-anhydride and Cbz-Cl, respectively. The acylation of phenols is slow enough to allow chemoselective acylation of alcohols and amines in the presence of phenols.
- Yadav, Veejendra K.,Babu, K. Ganesh
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p. 577 - 580
(2007/10/03)
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