- Iron-Catalyzed Enantioselective Radical Carboazidation and Diazidation of α,β-Unsaturated Carbonyl Compounds
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Azidation of alkenes is an efficient protocol to synthesize organic azides which are important structural motifs in organic synthesis. Enantioselective radical azidation, as a useful strategy to install a C-N3 bond, remains challenging due to the inherently instability and unique structure of radicals. Here, we disclose an efficient enantioselective radical carboazidation and diazidation of α,β-unsaturated ketones and amides catalyzed by chiral N,N′-dioxide/Fe(OTf)2 complexes. An array of substituted alkenes was transformed to the corresponding α-azido carbonyl derivatives in good to excellent enantioselectivities, benefiting the preparation of chiral α-amino ketones, vicinal amino alcohols, and vicinal diamines. Control experiments and mechanistic studies proved the radical pathway in the reaction process. The DFT calculations showed that the azido transferred to the radical intermediate via an intramolecular five-membered transition state with the internal nitrogen of the Fe-N3 species.
- Dong, Shunxi,Feng, Xiaoming,He, Jun,Liu, Wen,Liu, Xiaohua,Pu, Maoping,Wu, Yun-Dong,Zhang, Tinghui
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p. 11856 - 11863
(2021/08/16)
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- Two-Step One-Pot Synthesis of Unsymmetrical (Hetero)Aryl 1,2-Diketones by Addition-Oxygenation of Potassium Aryltrifluoroborates to (Hetero)Arylacetonitriles
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An efficient one-pot two-step procedure for the synthesis of unsymmetrical (hetero)aryl 1,2-diketones has been developed. The reaction proceeds through a palladium-catalyzed nucleophilic addition of potassium aryltrifluoroborates to aliphatic nitriles followed by a copper-catalyzed aerobic benzylic C–H oxygenation using molecular oxygen as a green oxidant. This represents the first example of the direct synthesis of unsymmetrical diaryl 1,2-diketones from arylacetonitriles. This method utilizes inexpensive, stable, nontoxic, and readily available starting materials, is highly effective in the presence of both electron-rich and electron-poor nitriles and aryltrifluoroborates, and tolerates a wide variety of functional groups. The synthetic utility of this transformation was shown by increasing the scale of the reaction and by carrying out the one-pot protocol for the preparation of quinoxaline and benzimidazole derivatives. A plausible reaction mechanism has also been proposed.
- Kumar, Yogesh,Jaiswal, Yogesh,Kumar, Amit
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p. 494 - 505
(2018/02/09)
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- Exploiting Aryl Mesylates and Tosylates in Catalytic Mono-α-arylation of Aryl- and Heteroarylketones
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The first general palladium catalyst for the catalytic mono-α-arylation of aryl- and heteroarylketones with aryl mesylates and tosylates is described. The newly developed indolyl-derived phosphine ligand L7 has been identified to promote this reaction eff
- Fu, Wai Chung,So, Chau Ming,Yuen, On Ying,Lee, Irene Toi Chuk,Kwong, Fuk Yee
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supporting information
p. 1872 - 1875
(2016/05/19)
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- Palladium-catalyzed α-arylation of arylketones at low catalyst loadings
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A general catalytic protocol for the α-arylation of aryl ketones has been developed. It involves the use of a preformed, bench-stable Pd-N-heterocyclic carbene pre-catalyst bearing IHept as an ancillary ligand, and allows the coupling of various functiona
- Marelli, Enrico,Corpet, Martin,Davies, Sian R.,Nolan, Steven P.
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supporting information
p. 17272 - 17276
(2015/02/05)
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- Palladium-catalyzed mono-α-arylation of carbonyl-containing compounds with aryl halides using dalphos ligands
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We report the extension and optimization of the [Pd(cinnamyl)Cl] 2/DalPhos catalyst system, previously found effective for the mono-α-arylation of acetone, to the mono-α-arylation of a variety of carbonyl-containing compounds with aryl halides and heteroaryl halides. Aryl methyl ketones, heteroaryl methyl ketones, propiophenones, malonates, and methoxyacetone can be α-arylated under relatively mild conditions and in good yields. We also report the limitations of the ligand/catalyst system towards other classes of carbonyl-containing compounds. We report the application of the [Pd(cinnamyl)Cl]2/DalPhos catalyst system, previously found effective for the mono-α-arylation of acetone, to the mono-α-arylation of a variety of carbonyl-containing compounds with aryl halides and heteroaryl halides.
- Crawford, Sarah M.,Alsabeh, Pamela G.,Stradiotto, Mark
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p. 6042 - 6050,9
(2020/09/02)
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- A simple method for the synthesis of substituted benzylic ketones: Homologation of aldehydes via the in situ generation of aryldiazomethanes from aromatic aldehydes
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A general method for the homologation of aldehydes to benzylic ketones has been developed. Aryldiazomethanes were generated in situ in the presence of an aldehyde by simply heating the tosylhydrazones of aromatic aldehydes in the presence of a stoichiometric amount of base in polar protic solvents. The resulting polar protic solvent promoted homologation afforded benzylic ketones in moderate to excellent yields with a variety of aldehydes. Isolation of the tosylhydrazones was not necessary; they could be prepared in ethanol and carried through the sequence without isolation. This methodology allows easy access to a wide variety of substituted aryldiazomethanes that would be difficult, or even impossible, to prepare via conventional methods and circumvents the toxicity and stability problems associated with the isolation and/or handling solutions of aryldiazomethanes.
- Angle, Steven R.,Neitzel, Martin L.
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p. 6458 - 6461
(2007/10/03)
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- The reaction of arylaldehydes with hexamethylphosphorous triamide and the use of the resulting products for the synthesis of enamines and deoxybenzoins
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The reaction between the arylaldehydes 1a,b and hexamethylphosphorous triamide 2 leads to the [aryl(dimethylamino)methyl]phosphonic bis(dimethylamides) 3a,b. These can be easily deprotonated by butyllithium in 1,2-dimethoxyethane and condensed with arylaldehydes to afford enamines 4a-f or deoxybenzoins 5a-f in fair to good yield.
- Babudri,Fiandanese,Musio,Naso,Sciavovelli,Scilimati
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p. 225 - 228
(2007/10/02)
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- Stereoselective Synthesis of an Analogue of Podophyllotoxin by an Intramolecular Diels-Alder Reaction
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The dihydrobenzocyclobutene 90 having a 4-hydroxycrotonate unit attached via an ester linkage as an internal dienophile can be cyclized to a 3:1 mixture of the trans lactone 92 (an analogue of podophyllotoxin, 1) and the cis lactone 93.This stereoselective reaction proceeds via the intermediacy of the o-quinodimethane 91 which cyclizes from the endo transition state 91n in preference to the exo-one 91x, presumably because of stabilization of the former by secondary orbital overlap.This result provides evidence that a proposed general route to the synthesis of podophyllotoxin, 1, and its analogues via the internal cycloaddition of the o-quinodimethane 8 to 9n may prove successful.Several possible approaches to the synthesis of the trans-2-aryldihydrobenzocyclobutenol 4 are described.The benzyne 11 was prepared and underwent but no cycloadditions.Although the 2-bromobenzocyclobutenone 23 could be synthesized in an efficient manner, it proved impossible to convert it into 4 by means of the aryl organometallic reagents 22ab.The bromo epoxide 52 was prepared and subjected to metal-halogen exchange and Lewis acid catalyzed epoxide rearrangement in an attempt to prepare 4.The aldehyde 56 was obtained in this reaction, clearly indicating that the desired intermediate 54 had been formed but could not be trapped under these conditions.Two ring contraction routes to 4 are also described, both beginning with the 1-indanone 74 prepared in good yield from piperonal 14.The diol monomesylate 78, prepared from 74, suffered base-catalyzed E2 elimination rather than the desired rearrangement to 80.The diazo ketone 83 underwent Wolff rearrangement to give the desired ester 84, but only in 7percent yield.Two interesting transformations were observed in these ring contraction schemes, namely the formation of the oxathiole dioxide 77 on mesylation of the ketol 75 and the preparation of the diazirene 86 on photolysis of the diazo ketone 83 at long wavelengths.The ester 84 was then saponified to the acid 87 which was coupled with methyl 4-hydroxycrotonate, 5, to give 90.The assignment of the structures of the products of thermolysis of 90 was based on high field 1H NMR and analogy to the spectra of similar compounds in the literature.
- Jung, Michael E.,Lam, Patrick Yuk-Sun,Mansuri, Muzzamil M.,Speltz, Laurine M.
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p. 1087 - 1105
(2007/10/02)
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