- C-C Bond Cleavage of Unactivated 2-Acylimidazoles
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2-Acylimidazoles are widely used as post-Transformable carboxylic acid equivalents in chemoselective and enantioselective reactions. Their transformations, however, require pretreatment with highly reactive, toxic methylating reagents to facilitate C-C bond cleavage. Here, we demonstrate that such pretreatment can be avoided and the C-C bond cleaved under neutral conditions without the use of additional reagents or catalysts. The scope of the reaction, including the use of products reported in the literature as substrates, and some mechanistic insights are described.
- Xin, Hai-Long,Pang, Bo,Choi, Jeesoo,Akkad, Walaa,Morimoto, Hiroyuki,Ohshima, Takashi
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p. 11592 - 11606
(2020/10/23)
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- Pd-Catalyzed Regioselective Hydroesterification of Olefins with 2,2,2-Trifluoroethyl Formate
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A Pd-catalyzed regioselective hydroesterification of olefins with 2,2,2-trifluoroethyl formate (TFEF) is described. Either linear or branched esters can be selectively obtained with proper ligands in most cases. The reaction process is operationally simple and involves no toxic CO gas.
- Chen, Jinhua,Chu, Jianxiao,Huang, Minyan,Ren, Wenlong,Shi, Yian
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supporting information
(2020/03/04)
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- Catalytic, Enantioselective β-Protonation through a Cooperative Activation Strategy
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The NHC-catalyzed transformation of unsaturated aldehydes into saturated esters through an organocatalytic homoenolate process has been thoroughly studied. Leveraging a unique “Umpolung”-mediated β-protonation, this process has evolved from a test bed for homoenolate reactivity to a broader platform for asymmetric catalysis. Inspired by our success in using the β-protonation process to generate enals from ynals with good E/Z selectivity, our early studies found that an asymmetric variation of this reaction was not only feasible, but also adaptable to a kinetic resolution of secondary alcohols through NHC-catalyzed acylation. In-depth analysis of this process determined that careful catalyst and solvent pairing is critical for optimal yield and selectivity; proper choice of nonpolar solvent provided improved yield through suppression of an oxidative side reaction, while employment of a cooperative catalytic approach through inclusion of a hydrogen bond donor cocatalyst significantly improved enantioselectivity.
- Wang, Michael H.,Barsoum, David,Schwamb, C. Benjamin,Cohen, Daniel T.,Goess, Brian C.,Riedrich, Matthias,Chan, Audrey,Maki, Brooks E.,Mishra, Rama K.,Scheidt, Karl A.
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p. 4689 - 4702
(2017/05/12)
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- Pd-catalyzed aldehyde to ester conversion: A hydrogen transfer approach
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Aliphatic and aromatic aldehydes are successfully converted into their corresponding esters using Pd(OAc)2 and XPhos. This approach utilizes a hydrogen transfer protocol: concomitant reduction of acetone to isopropanol provides an inexpensive and sustainable approach that mitigates the need for other oxidants.
- Tschaen, Brittany A.,Schmink, Jason R.,Molander, Gary A.
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supporting information
p. 500 - 503
(2013/04/11)
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- Rhodium(I)-catalyzed enantioselective 1,4-addition of nucleophilic silicon
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A rhodium(I)-catalyzed activation of a silicon-boron linkage, that is, the transmetalation of silicon from boron to rhodium(I) by means of an RhI-OH complex, enables the conjugate transfer of nucleophilic silicon onto α,β-unsaturated acceptors. Pre- or in situ formed cationic rhodium(I)-binap complexes catalyze this novel carbon-silicon bond formation with exceptional enantiocontrol, 92 to >99% ee for cyclic carbonyl and carboxyl compounds as well as >99% ee for acyclic carboxyl compounds.
- Walter, Christian,Fr?hlich, Roland,Oestreich, Martin
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scheme or table
p. 5513 - 5520
(2009/12/09)
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- An efficient method for the preparation of carboxamides by dehydration condensation using tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)silane
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The use of tetraalkoxysilanes, particularly tetrakis(perfluoroalkoxy) silanes, in dehydration condensation of carboxylic acids with amines was investigated. Tetrakis(1,1,1,3,3,3-hexafluoro-2-propoxy)silane, Si[OCH(CF 3)2]4, prepared easily from silicon tetrachloride and sodium 1,1,1,3,3,3-hexafluoro-2-propoxide, was found to be an effective dehydrating reagent for preparing various carboxamides in good to high yields from the corresponding carboxylic acids and amines. Copyright
- Tozawa, Takashi,Yamane, Yoshinobu,Mukaiyama, Teruaki
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p. 1586 - 1587
(2007/10/03)
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- Acid-Catalyzed Reaction of 2,2,2-Trifluorodiazoethane for Analysis of Functional Groups by 19F Nuclear Magnetic Resonance Spectrometry
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The acid-catalyzed reactions of trifluorodiazoethane with alcohols, phenols, thiols, and carboxylic acids are reported.The yield data for these trifluoroethyl derivatives suggest a simple, and in many cases, quantitative method for introduction of a fluorine tagging group.The 19F chemical shifts indicate that most functional groups (e.g., phenols, alcohols, etc.) have fairly well resolved chemical shifts regions.In addition, paramagnetic shift reagents have been utilized to selectively differentiate carboxylic acids from other active hydrogen functional groups.
- Koller, K. L.,Dorn, H. C.
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p. 529 - 533
(2007/10/02)
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