6906-32-7Relevant academic research and scientific papers
Facile Installation of 2-Reverse Prenyl Functionality into Indoles by a Tandem N-Alkylation-Aza-Cope Rearrangement Reaction and Its Application in Synthesis
Chen, Xiaobei,Fan, Huaqiang,Zhang, Shilei,Yu, Chenguang,Wang, Wei
supporting information, p. 716 - 723 (2016/01/12)
An unprecedented tandem N-alkylation-ionic aza-Cope (or Claisen) rearrangement-hydrolysis reaction of readily available indolyl bromides with enamines is described. Due to the complicated nature of the two processes, an operationally simple N-alkylation and subsequent microwave-irradiated ionic aza-Cope rearrangement-hydrolysis process has been uncovered. The tandem reaction serves as a powerful approach to the preparation of synthetically and biologically important, but challenging, 2-reverse quaternary-centered prenylated indoles with high efficiency. Notably, unusual nonaromatic 3-methylene-2,3-dihydro-1H-indole architectures, instead of aromatic indoles, are produced. Furthermore, the aza-Cope rearrangement reaction proceeds highly regioselectively to give the quaternary-centered reverse prenyl functionality, which often produces a mixture of two regioisomers by reported methods. The synthetic value of the resulting nonaromatic 3-methylene-2,3-dihydro-1Hindole architectures has been demonstrated as versatile building blocks in the efficient synthesis of structurally diverse 2-reverse prenylated indoles, such as indolines, indolefused sultams and lactams, and the natural product bruceolline D.
Development and mechanistic investigation of a highly efficient iridium(V) silyl complex for the reduction of tertiary amides to amines
Park, Sehoon,Brookhart, Maurice
experimental part, p. 640 - 653 (2012/03/13)
The cationic Ir(III) acetone complex (POCOP)Ir(H)2(acetone) + (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) was shown to catalyze the reduction of a variety of tertiary amides to amines using diethylsilane as reductant. Mechanistic studies established that a minor species generated in the reaction, the neutral silyl trihydride Ir(V) complex (POCOP)IrH3(SiEt2H), was the catalytically active species. High concentrations of this species could be conveniently generated by treatment of readily available (POCOP)IrHCl with tert-butoxide in the presence of Et2SiH2 under H2. Thus, using this mixture in the presence of a trialkylammonium salt, a wide array of tertiary amides, including extremely bulky substrates, are rapidly and quantitatively reduced to tertiary amines under mild conditions with low catalyst loading. A detailed mechanistic study has been carried out and intermediates identified. In brief, (POCOP)IrH3(SiEt2H) reduces the amide to the hemiaminal silyl ether that, in the presence of a trialkylammonium salt, is ionized to the iminium ion, which is then reduced to the tertiary amine by Et 2SiH2. Good functional group compatibility is demonstrated, and a high catalyst stability has provided turnover numbers as high as 10 000.
Supramolecular catalysis of unimolecular rearrangements: Substrate scope and mechanistic insights
Fiedler, Dorothea,Van Halbeek, Herman,Bergman, Robert G.,Raymond, Kenneth N.
, p. 10240 - 10252 (2007/10/03)
A cavity-containing metal-ligand assembly is employed as a catalytic host for the 3-aza Cope rearrangement of allyl enammonium cations. Upon binding, the rates of rearrangement are accelerated for all substrates studied, up to 850-fold. Activation parameters were measured for three enammonium cations in order to understand the origins of acceleration. Those parameters reveal that the supramolecular structure is able to reduce both the entropic and enthalpic barriers for rearrangement and is highly sensitive to small structural changes of the substrate. The space-restrictive cavity preferentially binds closely packed, preorganized substrate conformations, which resemble the conformations of the transition states. This hypothesis is also supported by quantitative NOE studies of two encapsulated substrates, which place the two reacting carbon atoms in close proximity. The capsule can act as a true catalyst, since release and hydrolysis facilitate catalytic turnover. The question of product hydrolysis was addressed through detailed kinetic studies. We conclude that the iminium product must dissociate from the cavity interior and the assembly exterior before hydroxide-mediated hydrolysis, and propose the intermediacy of a tight ion pair of the polyanionic host with the exiting product.
Formation of azomethine ylids by thermolysis of oxazolidines. Study of the reaction in solution and in the gaseous phase
Bureau, R.,Mortier, J.,Joucla, M.
, p. 584 - 596 (2007/10/02)
Thermolysis of oxazolidines leads to azomethine ylids via cycloreversion.In the liquid phase, these intermediates then give 1-3 dipolar cycloaddition; in the gaseous phase, they lead to aziridines.With an alkyl group in position 2, we observed also the formation of enamines.The effect of substituents on both the cycloreversion reaction and the evolution of azomethine ylids was studied.The mechanism of the process tautomerism aziridine -> azomethine ylid -> enamine is discussed.Keywords - azomethine ylids / oxazolidines / cycloreversion / aziridines / enamines / tautomerism
Flash vacuum thermolysis of 2-isopropyl oxazolidines. Mechanism of the tautomerism between azomethine ylid, aziridine and enamine
Bureau, Ronan,Joucla, Marc
, p. 6017 - 6020 (2007/10/02)
Depending on the nature of the substitution of 2-isopropyl oxazolidines and the Flash Vacuum Thermolysis conditions, aziridines and/or enamines are recovered through the azomethine ylid formed in situ Studies with deuterium labelled molecules give arguments for a concerted process in the gas phase.
HIGHLY ENANTIOSELECTIVE ISOMERIZATION OF PROCHIRAL ALLYLAMINES CATALYZED BY CHIRAL DIPHOSPHINE RHODIUM(I) COMPLEXES. PREPARATION OF OPTICALLY ACTIVE ENAMINES
Tani, Kazuhide,Yamagata, Tsuneaki,Akutagawa, Susumu,Kumobayashi, Hidenori,Taketomi, Takanao,et al.
, p. 5208 - 5217 (2007/10/02)
Rh(I) complexes of types ClO4 and n>ClO4 (diphosphine = cis-chelating tertiary diphosphine; diene = 1,5-cyclooctadiene or norbornadiene; S = solvent) were found to be effective catalists for allylic hydrogen migration of tertiary and secondary allylamines to give the corresponding (E)-enamines and imines, respectively.Studies on diphosphine ligands with respect to the catalytic activity and product selectivity led to the discovery of a fully aryl-substituted diphosphine, BINAP , which produces very active Rh(I) complex catalysts.With ClO4 (COD = 1,5-cyclooctadiene) or n>ClO4 as catalyst, (Z)-(diethylnerylamine, 1) or (E)-N,N-diethyl-3,7-dimethyl-2,6-octadienylamine (diethylgeranylamine, 2) was isomerized into the racemic (E)-enamine (E)-N,N-diethyl-3,7dimethyl-1,6-octadienylamine (citronellenamine, 3) with a chemical selectivity of over 95percent, the 6-double bond being retained intact.A variety of substituted allylamines serves as the substrate, e.g., (E)-N,N-dimethyl-2-butenylamine, N,N-dimethyl-2-methyl-2-propenylamine, N,N-dimethyl-3-methyl-2-butenylamine, N,N-dimethyl-3-phenyl-2-butenylamine.Asymmetric isomerization of prochiral allylamines producing optically active enamines or imines can be effected with cationic Rh(I) complexes of various chiral diphosphine ligands such as (2R,3R)-DIOP and others.The ligand that gives the highest optical yield was (+)- or (-)-BINAP.Virtually perfect enantioselectivity (95-99percent ee) was achieved with + for the isomerization of 1 or 2 into the optically active (E)-enamine (3).A clear stereochemical correlation was established between the olefin geometry (E or Z) of substrates, the configuration of the chiral diphosphines (R or S), and the chiral carbon configuration of the product enamines (R or S).The present catalytic system thus provides a convenient and practical access to optically active aldehydes.For example, optically pure natural citronellal can be produced either from nerylamine with the Rh(I)-(+)-BINAP catalyst or from geranylamine with the Rh(I)-(-)-BINAP complex catalyst.
Proton Affinities and the Site of Protonation of Enamines in the Gas Phase
Ellenberger, Mark R.,Dixon, David A.,Farneth, William E.
, p. 5377 - 5382 (2007/10/02)
The gas-phase proton affinities of a number of methyl-substituted enamines and imines have been measured using ion cyclotron resonance spectroscopy.Comparison of the effect of substituents on the proton affinities of the enamines with those of corresponding amines is used to show that protonation in the gas phase occurs at carbon leading to the formation of an iminium ion.The observation of a large substituent effect for substitution of an α-methyl group also suggests that there is a significant amount of delocalization of positive charge in the iminium ion.A comparison with solution-phase basicities of enamines is also presented.
Mechanism of Hydrolysis of N-(1-Aminoalkyl) Amides
Loudon, G. Marc,Almond, Merrick R.,Jacob, James N.
, p. 4508 - 4515 (2007/10/02)
Many of the title compounds (structure 1) are remarkably stable to hydrolysis and can be isolated and characterized.The pH-rate profile for hydrolysis of the title compounds involves plateaus in the acid and base region, with the rate of hydrolysis in the basic region somewhat faster.The compounds hydrolyze to amides, aldehydes, and ammonia; the intermediacy of an imine in the basic region is demonstrated by its trapping with added CN-.An optically active derivative of 1 hydrolyzes and loses optical activity at about the same rate in both the acidic and basic regions of pH.The reaction is characterized in basic solution by highly positive activation entropies, and alkylation of the amino nitrogen increases the rate significantly.The hydrolysis reaction shows no detectable buffer catalysis at any pH studied.The hydrolysis reaction is very sensitive to the amide leaving group; electron-withdrawing substituents on the amide portion of 1 substantially increase the rate of hydrolysis.The mechanism of hydrolysis in basic solution seems to be best described as a unimolecular solvolysis with an amide anion as a leaving group (Scheme I).In acidic solution the most likely mechanism of hydrolysis (Scheme II) appears to involve the expulsion of an amide enol (imidic acid).The implications of these findings are discussed for situation in which compounds of type 1 have found utility.
