- Photoredox Catalytic Phosphite-Mediated Deoxygenation of α-Diketones Enables Wolff Rearrangement and Staudinger Synthesis of β-Lactams
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A novel visible-light-driven catalytic activation of C=O bonds by exploiting the photoredox chemistry of 1,3,2-dioxaphospholes, readily accessible from α-diketones and trialkyl phosphites, is reported. This mild and environmentally friendly strategy provides an unprecedented and efficient access to the Wolff rearrangement reaction which traditionally entails α-diazoketones as precursors. The resulting ketenes could be precisely trapped by alcohols/thiols to give α-aryl (thio)acetates and by imines to afford the valuable β-lactams in up to 99 % yields.
- Jiang, Zhiyong,Li, Haijun,Wei, Guo,Yang, Hui
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supporting information
p. 19696 - 19700
(2021/08/03)
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- Ester Formation via Symbiotic Activation Utilizing Trichloroacetimidate Electrophiles
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Trichloroacetimidates are useful reagents for the synthesis of esters under mild conditions that do not require an exogenous promoter. These conditions avoid the undesired decomposition of substrates with sensitive functional groups that are often observed with the use of strong Lewis or Br?nsted acids. With heating, these reactions have been extended to benzyl esters without electron-donating groups. These inexpensive and convenient methods should find application in the formation of esters in complex substrates.
- Mahajani, Nivedita S.,Meador, Rowan I. L.,Smith, Tomas J.,Canarelli, Sarah E.,Adhikari, Arijit A.,Shah, Jigisha P.,Russo, Christopher M.,Wallach, Daniel R.,Howard, Kyle T.,Millimaci, Alexandra M.,Chisholm, John D.
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p. 7871 - 7882
(2019/06/27)
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- A fast and practical synthesis of tert-butyl esters from 2-tert-butoxypyridine using boron trifluoride·diethyl etherate under mild conditions
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A practical direct preparation of tert-butyl esters from 2-tert-butoxypyridine has been developed. This system features the use of boron trifluoride·diethyl etherate in toluene solvent to rapidly achieve the reaction at room temperature. Using this reaction protocol, a variety of tert-butyl esters were synthesized from several different carboxylic acids at high yields. This practical procedure provides a promising and effective approach to the protection of carboxylic acids with a tert-butyl group.
- La, Minh Thanh,Kim, Hee-Kwon
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p. 3748 - 3754
(2018/05/28)
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- The Conversion of tert-Butyl Esters to Acid Chlorides Using Thionyl Chloride
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The reaction of tert-butyl esters with SOCl2 at room temperature provides acid chlorides in unpurified yields of 89% or greater. Benzyl, methyl, ethyl, and isopropyl esters are essentially unreactive under these conditions, allowing for the selective conversion of tert-butyl esters to acid chlorides in the presence of other esters.
- Greenberg, Jacob A.,Sammakia, Tarek
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p. 3245 - 3251
(2017/03/23)
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- Rhodium catalyzed arylation of diazo compounds with aryl boronic acids
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A general and efficient synthesis of diarylacetate, a diarylmethine derivative, was accomplished through rhodium catalyzed direct arylation of diazo compounds with arylboronic acids. The reaction tolerates various boronic acid derivatives and functional groups. Notably, chemoselective arylation of diazo compounds over other electrophiles were demonstrated. The efficacy of the developed methodology is shown by the expeditious synthesis of the core structure of diclofensine.
- Ghorai, Jayanta,Anbarasan, Pazhamalai
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p. 3455 - 3461
(2015/04/14)
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- Rh(I)-catalyzed cross-coupling of α-diazoesters with arylsiloxanes
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An Rh(I)-catalyzed cross-coupling of diazoesters with arylsiloxanes has been successfully achieved. This transformation is a new method for the construction of the C(sp3)-C(sp2) bond, thus providing an alternative synthesis of α-aryl esters. Rh(I)-carbene migratory insertion has been proposed to be involved in this coupling reaction. The reaction represents the first example of utilizing arylsiloxane as the coupling partner in the carbene-involved cross-coupling reactions.
- Xia, Ying,Liu, Zhen,Feng, Sheng,Ye, Fei,Zhang, Yan,Wang, Jianbo
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supporting information
p. 956 - 959
(2015/03/30)
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- Concave reagents, 21: Selective acylations of primary and secondary alcohols by ketenes
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Concave pyridines 1 were used to catalyze the addition of primary and secondary alcohols to ketenes 4, and the kinetic data of these catalyses were determined. In inter- and intramolecular competitions the use of 1e-g led to improved selectivities for the acylation of primary alcohols in comparison with secondary alcohols. All primary alcohols react at comparable rates. Observed rate constants were correlated with Taft's Es values. The starting materials and products were fully characterized. VCH Verlagsgesellschaft mbH, 1996.
- Schyja, Wolfgang,Petersen, Soenke,Luening, Ulrich
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p. 2099 - 2105
(2007/10/03)
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- A NEW GENERAL METHOD FOR THE PREPARATION OF CARBOXYLIC ACID ESTERS
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Esters can be generated directly in good yields under mild conditions from the corresponding carboxylic acid and alcohol in the presence of equivalent amounts of pyridine, triphenylphosphine and N-halosuccinimide.Key words: Carboxylic acids, esterification, triphenylphosphine, N-halo succinimides.
- Froeyen, Paul
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p. 145 - 152
(2007/10/02)
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- Activated Basic Alumina Promotes a Mild, Clean and High-Yield Racemization-Free Synthesis of t-Butyl Esters from Chiral Acid Bromides and t-Butyl Alcohol
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Esterification of a variety of acid bromides having even steric bulkiness with t-BuOH/activated basic alumina gave the corresponding t-butyl esters in good to excellent yields.In the case of chiral acid bromides, no racemization has been ascertained for the first time.
- Nagasawa, Kazuo,Ohhashi, Keiko,Yamashita, Asami,Ito, Keiichi
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p. 209 - 212
(2007/10/02)
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- Mechanism for Diacyl Peroxide Decomposition
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The presence of ion-pair intermediates in diacyl peroxide decomposition has been established.Various substituted (4-X-phenyl)phenylacetyl Y-benzoyl peroxides and three corresponding 4-X-benzhydryl-4-nitrobenzoic carbonic anhydrides (X = CH3, H, Cl) were prepared.All compounds decomposed in 90percent acetone-water (v/v), giving the ionic products ester, alkohol, and acid.The fraction of ester (R) was similar to that found in the solvolysis of substituted benzhydryl-N-nitrosoamides, indicating a similar spectrum of ion-pair intermediates.The yield of ester product could be increased markedly by the addition of common ion.The mixed carbonic carboxylic anhydrides were not products of peroxide decomposition in either nucleophilic or nonnucleophilic solvents and showed a lower decompositin rate than the peroxide.Lastly, both the peroxide and the mixed carbonic carboxylic anhydride decomposed in chloroform with net retention.Neither CIDNP nor any radical abstraction product was detected.
- Linhardt, R.J.,Murr, B.L.,Montgomery, E.,Osby, J.,Sherbine, J.
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p. 2242 - 2251
(2007/10/02)
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- Photostimulated Nucleophilic Aromatic Substitution for Halides with Carbon Nucleophiles. Preparative and Mechanistic Aspects
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The photo-SRN1 reaction operates efficiently with enolate anions derived from simple ketones and esters, but 2-lithio-1,3-dithiane gives low yields.The sluggish and inefficient reaction of dialkyl-substituted ketone and ester enolates is traced to hydrogen atom transfer from the carbon adjacent to the enolate anion to the transient phenyl radical.The first systematic survey of intramolecular coupling of keton enolate anions shows that six-, seven-, eight-, and ten-membered rings can be formed, although the β-hydrogen transfer becomes important in certain cases.
- Semmelhack, M. F.,Bargar, Thomas
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p. 7765 - 7774
(2007/10/02)
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