- Atroposelective Synthesis of Axially Chiral N-Arylpyrroles by Chiral-at-Rhodium Catalysis
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A transformation of fluxional into configurationally stable axially chiral N-arylpyrroles was achieved with a highly atroposelective electrophilic aromatic substitution catalyzed by a chiral-at-metal rhodium Lewis acid. Specifically, N-arylpyrroles were alkylated with N-acryloyl-1H-pyrazole electrophiles in up to 93 percent yield and with up to >99.5 percent ee, and follow-up conversions reveal the synthetic utility of this new method. DFT calculations elucidate the origins of the observed excellent atroposelectivity.
- Chen, Shuming,Han, Feng,Houk, K. N.,Ivlev, Sergei,Meggers, Eric,Xie, Xiulan,Ye, Chen-Xi
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supporting information
p. 13552 - 13556
(2020/06/05)
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- Is H Atom Abstraction Important in the Reaction of Cl with 1-Alkenes?
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The relative yields of products of the reaction of Cl atoms with 1-alkenes (C4-C9) were determined to see whether H atom abstraction is an important channel and if it is to identify the preferred position of abstraction. The presence of all the possible positional isomers of long chain alkenones and alkenols among the products, along with chloroketones and chloroalcohols, confirms the occurrence of H atom abstraction. A consistent pattern of distribution of abstraction products is observed with oxidation at C4 (next to allyl) being the lowest and that at CH2 groups away from the double bond being the highest. This contradicts with the higher stability of allyl (C3) radical. For a better understanding of the relative reactivity, ab initio calculations at MP2/6-311+G (d,p) level of theory are carried out in the case of 1-heptene. The total rate coefficient, calculated using conventional transition state theory, was found to be in good agreement with the experimental value at room temperature. The preferred position of Cl atom addition is predicted to be the terminal carbon atom, which matches with the experimental observation, whereas the rate coefficients calculated for individual channels of H atom abstraction do not explain the observed pattern of products. The distribution of abstraction products except at C4 is found to be better explained by reported structure activity relationship, developed from experimental rate coefficient data. This implies the reactions to be kinetically dictated and emphasizes the importance of secondary reactions.
- Walavalkar,Vijayakumar,Sharma,Rajakumar,Dhanya
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p. 4096 - 4107
(2016/07/06)
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- Three-step synthetic pathway to fused bicyclic hydantoins involving a selenocyclization step
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Sequential 5-alkenyl hydantoin and pyrrolidine ring-forming reactions have been applied in the synthesis of conformationally constrained fused bicyclic scaffold. They are assembled by a three-step reaction sequence from two variable building blocks (readily available β-ketoesters and alkenyl halides) by combining a Bucherer-Bergs reaction with a final selenium-promoted intramolecular cyclization as a key step. The chemoselectivity of this bicyclic hydantoin formation is strongly influenced by experimental factors such as the solvent and the use of additives. The reaction is regiospecific giving only five-membered fused bicyclic hydantoins in good to excellent yields stemming from the nucleophilic attack of the nitrogen atom to a cyclic seleniranium ion intermediate during the cyclization step. A separable diastereomeric mixture is obtained; the products with bridgehead substituents and phenylseleno groups in cis relationships were formed predominantly. The reaction tolerates a variety of substitution at the double bond, furthermore, the presence of substituents at C(5) and N(3) position opens up the capability of generating a broad structural diversity.
- ?mit, Biljana M.,Pavlovi?, Radoslav Z.
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p. 1101 - 1108
(2015/01/30)
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- 3,3′-Bis(trisarylsilyl)-substituted binaphtholate rare earth metal catalysts for asymmetric hydroamination
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Chiral 3,3′-bis(trisarylsilyl)-substituted binaphtholate rare earth metal complexes (R)-[Ln{Binol-SiAr3}(o-C6H 4CH2NMe2)(Me2NCH2Ph)] (Ln = Sc, Lu, Y; Binol-SiAr3 = 3,3′-bis(trisarylsilyl)-2,2′- dihydroxy-1,1′-binaphthyl; Ar = Ph (2-Ln), 3,5-xylyl (3-Ln)) and (R)-[La{Binol-Si(3,5-xylyl)3}{E(SiMe3)2}(THF) 2] (E = CH (4a), N (4b)) are accessible via facile arene, alkane, and amine elimination. They are efficient catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, giving TOF of up to 840 h -1 at 25 °C for 2,2-diphenyl-pent-4-enylamine (5c) using (R)-2-Y. Enantioselectivities of up to 95% ee were achieved in the cyclization of 5c with (R)-2-Sc. The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, but rates depend on total amine concentrations. Activation parameters for the cyclization of pent-4-enylamine using (R)-2-Y (ΔH(S)? = 57.4-(0.8) kJ mol-1 and ΔS(S)? = -102(3) J K-1 mol-1; ΔH(R)? = 61.5(0.7) kJ mol-1 and ΔS(R)? = -103(3) J K-1 mol -1) indicate a highly organized transition state. The binaphtholate catalysts were also applied to the kinetic resolution of chiral α-substituted aminoalkenes with resolution factors f of up to 19. The 2,5-disubstituted aminopentenes were formed in 7:1 to ≥50:1 trans diastereoselectivity, depending on the size of the α-substituent of the aminoalkene. Rate studies with (S)-1-phenyl-pent-4-enylamine ((S)-15e) gave the activation parameters for the matching (ΔH? = 52.2(2.8) kJ mol -1, ΔS? = -127(8) J K-1 mol-1 using (S)-2-Y) and mismatching (ΔH? = 57.7(1.3) kJ mol -1, ΔS? = -126(4) J K-1 mol-1 using (R)-2-Y) substrate/catalyst combination. The absolute configuration of the Mosher amide of (2S)-2-methyl-4,4-diphenyl-pyrrolidine and (2R)-methyl-(5S)- phenyl-pyrrolidinium chloride, prepared from (S)-15e, were determined by crystallographic analysis. Catalyst (R)-4a showed activity in the anti-Markovnikov addition of n-propylamine to styrene.
- Gribkov, Denis V.,Hultzsch, Kai C.,Hampel, Frank
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p. 3748 - 3759
(2007/10/03)
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- Cp*Ru(PN) complex-catalyzed isomerization of allylic alcohols and its application to the asymmetric synthesis of muscone
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Highly efficient isomerization of allylic alcohols into saturated carbonyls is accomplished using the catalyst system of Cp*RuCl[Ph2P(CH2)2NH2-κ2-P,N]-KOt-Bu (Cp* = η5-C5(CH3)5) under mild conditions. Mechanistic consideration based on isotope-labeling experiments indicated the present reaction is applicable to the asymmetric isomerization of racemic sec-allylic alcohols with a prochiral olefin via dynamic kinetic resolution. A concise asymmetric synthesis of muscone has been achieved, where the asymmetric isomerization using an optically active ligand is a key reaction. Copyright
- Ito, Masato,Kitahara, Sachiko,Ikariya, Takao
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p. 6172 - 6173
(2007/10/03)
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- Palladium Catalyzed Alternating Cooligomerization of Ethylene and Carbon Monoxide to Unsaturated Ketones
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Cationic palladium catalysts have been used to cooligomerize ethylene and carbon monoxide.At high ethylene/CO ratios (m/m = 10:1) in methylene chloride as a solvent, unsaturated alternating cooligomers of the general structure RmH (m >/= 1; R = CH2=CH-, CH2=CHCH2CH2- and CH3CH=CHCH2-) were obtained for the first time.Single component catalyst precursors X)>(1+)Y(1-) (PX = Ph2P(CH2)nC(=O)OR, Ph2P(CH2)2P(=O)Ph2, , Ph2P(CH2)2S(=O)Ph, n = 1-3, R = Me, Et; Y(1-) = BF4(1-), SbF6(1-)) with bidentate P,O- and P,S-ligands as well as in situ catalysts with unfunctionalized phosphine ligands were used.With PnBu3 as a ligand, selectivities for ethylvinylketone of 40percent based on the CO converted were obtained.The hemilabile phosphino-ester and phosphino-thiophene ligands behave like monodentate phosphines under catalytic conditions. - Keywords: Cooligomerization, Carbonylation, Palladium, Hemilabile, Unsaturated Ketone
- Keim, Wilhelm,Maas, Heiko,Mecking, Stefan
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p. 430 - 438
(2007/10/02)
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- Regioselective Aza-Cope Rearrangement of α-Halogenated and Nonhalogenated Imines
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The 3-aza-Cope rearrangement of α-halogenated and nonhalogenated ketimines by deprotonation of the corresponding iminium salts was found to be an especially facile and regioselective process.Deuterium labeling studies supported the proposed mechanism which required the rearrangement to be highly concerted.
- Welch, John T.,Corte, Bart De,Kimpe, Norbert De
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p. 4981 - 4983
(2007/10/02)
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- The Key Role of Water in the Heterogeneous Permanganate Oxidation of ω-Hydroxy Alkenes
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Potassium permanganate-copper sulphate in dichloromethane in the presence of a catalytic amount of water effects a smooth oxidative cyclization of ω-hydroxy alkenes to ω-lactones in good yields with the net loss of one or more carbon atoms in the procees.
- Baskaran, Sundarababu,Islam, Imadul,Vankar, Padma S.,Chandrasekaran, Srinivasan
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p. 1670 - 1671
(2007/10/02)
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- CYCLIZATION OF AMINYL RADICALS GENERATED BY ANODIC OXIDATION OF LITHIUM ALKENYLAMIDES. STEREO- AND REGIOSELECTIVE SYNTHESIS OF cis-1-ALKYL-2,5-DISUBSTITUTED PYRROLIDINES
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Neutral aminyl radicals (3) generated by anodic oxidation of lithium alkenylamides (2) were found to undergo a stereo- and regioselective cyclization to give cis-1-alkyl-2,5-disubstituted pyrrolidines (5c-5h) in moderate yields.The cis stereochemistry of 5c-5h was confirmed by comparison with the corresponding trans-1-alkyl-2,5-disubstituted pyrrolidines which were prepared by aminomercuration of 1c-1h.The structure of trans-1,2-dimethyl-5-phenylpyrrolidine (17) was established by an X-ray crystallographic analysis of its ammonium bromide 21.Various aminyl radicals examined in this study were found to combine exclusively with the internal carbon of their double bond to give a five- (5a-5h) or six-membered ring (13).No product arising from the cyclization is obtained from N-methyl-1-phenylbut-3-enylamine (14).
- Tokuda, Masao,Yamada, Yasufumi,Takagi, Toshiya,Suginome, Hiroshi,Furusaki, Akio
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p. 281 - 296
(2007/10/02)
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- SUBSTITUENT DIRECTED OXIDATIVE CYCLIZATION WITH CETYLTRIMETHYLAMMONIUM PERMANGANATE: A GENERAL APPROACH TO THE SYNTHESIS OF γ- AND δ-LACTONES
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Treatment of primary, secondary or tertiary γ- and δ-hydroxyolefins with cetyltrimethylammonium permanganate gives good yields of γ- and δ-lactones by oxidative cyclization, with loss of one carbon.
- Rathore, Rajendra,Vankar, Padma S.,Chandrasekaran, S.
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p. 4079 - 4082
(2007/10/02)
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- AMINYL RADICAL CYCLIZATION BY MEANS OF ANODIC OXIDATION. STEREOSELECTIVE SYNTHESIS OF cis-1-METHYL-2,5-DISUBSTITUED PYRROLIDINES
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Neutral aminyl radicals generated by anodic oxidation of lithium alkenylamides 2 undergo a stereoselective cyclization to give cis-1-methyl-2,5-disubstituted pyrrolidines 4.Their cis stereochemistry was confirmed by a comparison with trans-1,2-dimethyl-5-phenylpyrrolidine, the structure of which was established by X-ray crystallographic analysis of its quarternary ammonium bromide 6.
- Tokuda, Masao,Yamada, Yasufumi,Takagi, Toshiya,Suginome, Hiroshi,Furusaki, Akio
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p. 6085 - 6088
(2007/10/02)
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- RHODIUM CATALYZED HYDROACYLATION OF ETHYLENE WITH 4-PENTENALS. REACTIONS OF 4-HEXENAL-1-d
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A catalyst derived from 2,4-pentanedionatobis(ethylene)rhodium(I), I, promoted the addition of 4-pentenal to ethylene.The reaction was accompanied by the formation of double bond migration products derived from the 4-pentenal reactant and from the 6-hepten-3-one primary product.Compound I accomplished the addition of 4-hexenal to ethylene to afford high yields of 6-octen-3-one.The fate of the aldehyde hydrogen in this transformation has been determined in experiments employing 4-hexenal-1-d as reactant.Treatment of 4-hexenal-1-d with I in CHCl3 and CDCl3 afforded 6-octen-3-one possesing > 50percent d0 molecules while the isotopic composition of recovered unexpended 4-hexenal remained > 96percent d1. 6-Octen-3-one products with isotopic compositions of > 66percent d0 were afforded when ethylene was introduced to reaction mixtures.The location of deuterium in 6-octen-3-one, derived from treatment of 4-hexenal-1-d with I in the absence of added C2H4, was determined to be distributed at C-1 and C-2 and at the C=C bond by analysis of the 1H and 2H NMR spectra.Unexpended ethylene was recovered and was found to contain a substantial amount of deuterium.Mechanistic implications of these results are discussed.
- Vora, Krishnakant P.,Lochow, Charles F.,Miller, Roy G.
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p. 257 - 264
(2007/10/02)
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