- Aza-Matteson Reactions via Controlled Mono-and Double-Methylene Insertions into Nitrogen-Boron Bonds
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Boron-homologation reactions represent an efficient and programmable approach to prepare alkylboronates, which are valuable and versatile synthetic intermediates. The typical boron-homologation reaction, also known as the Matteson reaction, involves formal carbenoid insertions into C-B bonds. Here we report the development of aza-Matteson reactions via carbenoid insertions into the N-B bonds of aminoboranes. By changing the leaving groups of the carbenoids and altering Lewis acid activators, selective mono- and double-methylene insertions can be realized to access various α- and β-boron-substituted tertiary amines, respectively, from common secondary amines. The derivatization of complex amine-containing bioactive molecules, diverse functionalization of the boronate products, and sequential insertions of different carbenoids have also been achieved.
- Xie, Qiqiang,Dong, Guangbin
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supporting information
p. 14422 - 14427
(2021/09/29)
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- Ru-Catalyzed Switchable N-Hydroxyethylation and N-Acetonylation with Crude Glycerol
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Highly efficient Ru-catalyzed selective C?C or C?O bond cleavage of polyols (e.g., crude glycerol) for N-hydroxyethylation or N-acetonylation of amines was achieved through the hydrogen-borrowing approach. A variety of amines were transformed to the desired amino alcohols/ketones in moderate-to-excellent yields, opening up new avenues for generation of oxygenated pharmaceuticals and fine chemicals from renewable raw materials. The use of new redox-active catalysts containing bisphosphine/thienylmethylamine ligands allows this hydrogen-borrowing system to be operated selectively under both basic and acidic conditions.
- Xin, Zhuo,Jia, Le,Huang, Yuxing,Du, Chen-Xia,Li, Yuehui
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p. 2007 - 2011
(2020/03/19)
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- Palladium-catalyzed intramolecular carbene insertion into C(sp3)-H bonds
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A palladium-catalyzed carbene insertion into C(sp3)-H bonds leading to pyrrolidines was developed. The coupling reaction can be catalyzed by both Pd0 and PdII, is regioselective, and shows a broad functional group tolerance. This reaction is the first example of palladium-catalyzed C(sp3)-C(sp3) bond assembly starting from diazocarbonyl compounds. DFT calculations revealed that this direct C(sp3)-H bond functionalization reaction involves an unprecedented concerted metalation-deprotonation step. Pd in action: Palladium has been used to catalyze the C(sp3)-H insertion of metal carbenoids derived from α-diazoesters to form pyrrolidines through intramolecular assembly of C(sp3)-C(sp3) bonds. A reaction mechanism involving a metalation-deprotonation step instead of the usual concerted but asynchronous process is proposed.
- Solé, Daniel,Mariani, Francesco,Bennasar, M.-Llu?sa,Fernández, Israel
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p. 6467 - 6470
(2016/06/01)
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- A Direct C-H/Ar-H Coupling Approach to Oxindoles, Thio-oxindoles, 3,4-Dihydro-1 H-quinolin-2-ones, and 1,2,3,4-Tetrahydroquinolines
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A copper(II)-catalysed approach to oxindoles, thio-oxindoles, 3,4-dihydro-1H-quinolin-2-ones, and 1,2,3,4-tetrahydroquinolines via formal C-H, Ar-H coupling is described. In a new variant, copper(II) 2-ethylhexanoate has been identified as an inexpensive and efficient catalyst for this transformation, which utilises atmospheric oxygen as the re-oxidant. Copper(II) 2-ethylhexanoate: The synthesis of oxindoles, thio-oxindoles, 3,4-dihydro-1H-quinolin-2-ones, and 1,2,3,4-tetrahydroquinolines from linear precursors by direct C-H, Ar-H coupling by using a single copper catalyst is reported (see scheme; DIPEA=diisopropylethylamine, EWG=electron-withdrawing group). The cyclisations are simple to perform, run open to the air, are moisture insensitive, and use an inexpensive catalyst.
- Hurst, Timothy E.,Gorman, Ryan M.,Drouhin, Pauline,Perry, Alexis,Taylor, Richard J. K.
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supporting information
p. 14063 - 14073
(2016/02/18)
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- Dynamics of anilinium radical α-heterolytic fragmentation processes. Electrofugal group, substituent, and medium effects on desilylation, decarboxylation, and retro-aldol cleavage pathways
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A single electron transfer (SET) photosensitization technique in conjunction with time-resolved, laser spectroscopy has been employed to generate and kinetically analyze decay processes of anilinium radicals derived by one-electron oxidation of α-anilinocarboxylates, β- anilinoalcohols, and α-anilinosilanes. In this manner, the rates of unimolecular decarboxylation of aniliniumcarboxylate radicals were determined to be in the range 106 - 107 s-1 and dependent upon solvent polarity, the nature of the metal cation, and substituents on the aniline ring, nitrogen, and α-carbon. In addition, kinetic analysis of base-induced retro-aldol fragmentations of cation radicals arising by SET oxidation of β- anilinoalcohols has shown that they occur with bimolecular rate constants which vary from 104 to 105 M-1 s1. These values are close to those for α-deprotonation reactions of related N,N-dialkylanilinium radicals. The retro-aldol fragmentation rates, like those for α-decarboxylation, also vary in a patterned way with changes in arene ring, nitrogen, and α- and β- carbon substituents. An investigation of the dynamics of methanol-promoted reactions of α-(trimethylsilyl)methyl-substituted anilinium radicals, has demonstrated that a change in the nitrogen substituent from alkyl to acyl causes an ca. 10-fold increase in the desilylation rate. Parallel photochemical studies have been conducted to gain chemical evidence to support assignment of the anilinium radical decay pathways in the LFP experiments and to demonstrate the preparative consequences of the kinetic results. First, clean formation of products derived by coupling of the (N- methylanilino)methyl radical in photochemical reactions of 1,4- dicyanobenzene with either tetra-n-butylammonium N-methyl-N-phenylglycinate or β-(N-methyl-N-phenyl)aminoethanol shows that the respective decarboxylation and retro-aldol cleavage processes occur with exceptionally high efficiencies. Second, in accord with the high rates observed for aminium radical decarboxylation and base-induced retro-aldol fragmentation, tethered cyclohexenone - α-aminocarboxylates and - β-aminoethanols undergo high- yielding SET-promoted photocyclization reactions under both direct and SET- sensitized conditions. Last, results which depict how the rates of aminium radical α-fragmentation correlate with quantum efficiencies of SET-promoted reactions of tertiary amines and amides have come from a study of photocyclization reactions of N-(aminoethyl)- and (amidoethyl)phthalimides. The quantum yields for these SET-promoted processes are observed to vary with the electrofugal group and nitrogen substituent in the manner predicted on the basis of the LFP-determined fragmentation rates.
- Su, Zhuoyi,Mariano, Patrick S.,Falvey, Daniel E.,Yoon, Ung Chan,Oh, Sun Wha
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p. 10676 - 10686
(2007/10/03)
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