Direct Synthesis of Ternary Iminium Salts by Combination of Aldehydes or Ketones with Secondary Amine Salts<sup>1,2</sup>

Leonard, Nelson J.; Paukstelis, Joseph V.

doi:10.1021/jo01046a021

Cited by 148 publications

(48 citation statements)

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“…[PhNH=CHPh]SO 3 CF 3 : The NMR spectra were similar to those of the tetrafluoroborate analogue with an additional signal in the 13 1-(1-Phenylethylidene)pyrrolidinium tetrafluoroborate was prepared as described in the literature. [14] All other reagents were obtained from commercial sources and used as received. All new compounds described below are air-sensitive in solution.…”

Section: Methodsmentioning

confidence: 99%

Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes

Martı́n

Sola

Tejero

et al. 2006

Chemistry A European J

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Treatment of [Ir2(mu-H)(mu-Pz)2H3(NCMe)(PiPr3)2] (1) with one equivalent of HBF4 or [PhNH=CHPh]BF4 affords efficient catalysts for the homogeneous hydrogenation of N-benzylideneaniline. The reaction of 1 with HBF4 leads to the trihydride-dihydrogen complex [Ir2(mu-H)(mu-Pz)2H2(eta2-H2)(NCMe)(PiPr3)2]BF4 (2), which has been characterized by NMR spectroscopy and DFT calculations on a model complex. Complex 2 reacts with imines such as tBuN=CHPh or PhN=CHPh to afford amine complexes [Ir2(mu-H)(mu-Pz)2H2(NCMe){L}(PiPr3)2]BF4 (L = NH(tBu)CH2Ph, 3; NH(Ph)CH2Ph, 4) through a sequence of proton- and hydride-transfer steps. Dihydrogen partially displaces the amine ligand of 4 to form 2; this complements a possible catalytic cycle for the N-benzylideneaniline hydrogenation in which the amine-by-dihydrogen substitution is the turnover-determining step. The rates of ligand substitution in 4 and its analogues with labile ligands other than amine are dependent upon the nature of the leaving ligand and independent on the incoming ligand concentration, in agreement with dissociative substitutions. Water complex [Ir2(mu-H)(mu-Pz)2H2(NCMe)(OH2)(PiPr3)2]BF4 (7) hydrolyzes N-benzylideneaniline, which eventually affords the poor hydrogenation catalyst [Ir2(mu-H)(mu-Pz)2H2(NCMe)(NH2Ph)(PiPr3)2]BF4 (11). The rate law for the catalytic hydrogenation in 1,2-dichloroethane with complex [Ir2(mu-H)(mu-Pz)2H2(OSO2CF3)(NCMe)(PiPr3)2] (8) as catalyst precursor is rate = k[8]{p(H2)}; this is in agreement with the catalytic cycle deduced from the stochiometric experiments. The hydrogenation reaction takes place at a single iridium center of the dinuclear catalyst, although ligand modifications at the neighboring iridium center provoke changes in the hydrogenation rate. Even though this catalyst system is also capable of effectively hydrogenating alkenes, N-benzylideneaniline can be selectively hydrogenated in the presence of simple alkenes.

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Section: Methodsmentioning

confidence: 99%

Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes

Martı́n

Sola

Tejero

et al. 2006

Chemistry A European J

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“…-To initiate a systematic solid-state study the iminium ion salts derived from cinnamaldehyde and diaryl-prolinol derivatives, A and B, or imidazolidinones, C and D, were prepared by modifying the procedure of Leonard and Paukstelis [19], in which an ammonium salt, I, of a sec-amine is mixed with a carbonyl compound in EtOH or CH 2 Cl 2 (with or without Et 3 N catalysis). This yielded a precipitate or residue, which was washed and dried to give the iminium salts of correct elemental analyses (cf.…”

Section: (E)/(z)-isomericmentioning

confidence: 99%

“…and ammonium salts is assumed to be irreversible (Step a in Scheme 5; cf. Scheme 4), there are two extreme scenarios: i) If the (E)/(Z)-equilibrating rate (K eq ; Step b) is much slower than the rate of reaction with a nucleophile 19 ) (Step c), the enantiomer ratio (er) in the isolated product will be determined by the relative rate of (E)/(Z)-iminium-ion formation and the respective preference of Nu anti and Nu syn approach to the (E)/(Z)-diastereoisomeric iminium ions (Fig. 8); with exclusive Nu anti attack, er would be equal to k E /k Z .…”

Section: Kinetics Of the Formation Of Iminiummentioning

confidence: 99%

Stereochemical Models for Discussing Additions to α,β‐Unsaturated Aldehydes Organocatalyzed by Diarylprolinol or Imidazolidinone Derivatives – Is There an ‘(E)/(Z)‐Dilemma’?

Seebàch

Gilmour

Grošelj

et al. 2010

Helvetica Chimica Acta

102

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Dedicated to Professor Henri Kagan on the occasion of his 80th birthdayThe structures of iminium salts formed from diarylprolinol or imidazolidinone derivatives and a,bunsaturated aldehydes have been studied by X-ray powder diffraction ( Fig. 1), single-crystal X-ray analyses (Table 1), NMR spectroscopy (Tables 2 and 3, Figs. 2 -7), and DFT calculations (Helv. Chim. Acta 2009Acta , 92, 1, 1225Acta , 2010 Angew. Chem., Int. Ed. 2009, 48, 3065). Almost all iminium salts of this type exist in solution as diastereoisomeric mixtures with (E)-and (Z)-configured þ N¼C bond geometries. In this study, (E)/(Z) ratios ranging from 88 : 12 up to 98 : 2 (Tables 2 and 3) and (E)/(Z) interconversions (Figs. 2 -7) were observed. Furthermore, the relative rates, at which the (E)-and (Z)-isomers are formed from ammonium salts and a,b-unsaturated aldehydes, were found to differ from the (E)/(Z) equilibrium ratio in at least two cases (Figs. 4 and 5, a, and Fig. 6, a); more (Z)-isomer is formed kinetically than corresponding to its equilibrium fraction. Given that the enantiomeric product ratios observed in reactions mediated by organocatalysts of this type are often ! 99 : 1, the (E)-iminium-ion Helvetica Chimica Acta -Vol. 93 (2010) intermediates are proposed to react with nucleophiles faster than the (Z)-isomers (Scheme 5 and Fig. 8).Possible reasons for the higher reactivity of (E)-iminium ions (Figs. 8 and 9) and for the kinetic preference of (Z)-iminium-ion formation are discussed (Scheme 4). The results of related density functional theory (DFT) calculations are also reported (Figs. 10 -13 and Table 4).1. Introduction. -Since the renaissance of organocatalysis 6 ) in 2000 [3], this field has undergone an explosive development 7 ). Of the various types of organocatalysts, compounds with a sec-amino group (proline and its derivatives, including diarylprolinol ethers [5], and amino acid (mostly phenylalanine)-derived imidazolidinones [3b]) have experienced the widest use. They activate a-carbonyl positions for electrophilic attack 8 ) through enamines and b-carbonyl positions for nucleophilic attack through iminium ions, thus opening the door to enantioselectively catalyzed versions of the most important classical synthetic organic reactions 9 ). Entire sequences of such reactions can be performed with one organocatalyst, or with two different species, culminating in the formation of four and more stereogenic centers via so-called domino or cascade reactions [8]. However, much of the mechanistic intricacies of organocatalytic transformations remain unexplored; a casualty of the excitement that the synthetic competence of this class of small molecules has generated. Often reasonable mechanistic models are proposed that are based solely on the stereochemical outcome of the transformation in question.On closer inspection, aspects of many commonly accepted mechanistic models were identified that led to the proposal of possible alternatives. Thus, in proline catalysis, the role of oxazolidinones may not just be part of a parasiti...

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“…The procedure used was that established by Leonard and Paukstelis (32). Cyclophenanthrone (XXXV, 7.7 g.) was dis solved in hot absolute ethanol (45 ml.).…”

Section: -167° the Ultraviolet Spectrum Showed ^Toh 259^111mentioning

confidence: 99%

“…Support for the heteroannular diene structure comes from the work of Bowden et al (32), the quartet at 6.64, 6.88, 7.22 and 7.^6 "U due to the non-equivalent hydrogens of the methylene group adjacent to sulfur (33), the angular methyl singlet at 8.39'^ and the camphor sulfonic acid methyl sing lets at 8.90 and 9.221 . That the protonation actually occurs at C-6 rather than on nitrogen or at C-4 is supported by sev eral data.…”

mentioning

confidence: 98%

Photochemical studies on 4a-methyl-4,4a,9,10-tetrahydro-2(3H)-phenanthrone

Sieja

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Direct Synthesis of Ternary Iminium Salts by Combination of Aldehydes or Ketones with Secondary Amine Salts^1,2

Cited by 148 publications

References 0 publications

Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes

Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes

Stereochemical Models for Discussing Additions to α,β‐Unsaturated Aldehydes Organocatalyzed by Diarylprolinol or Imidazolidinone Derivatives – Is There an ‘(E)/(Z)‐Dilemma’?

Photochemical studies on 4a-methyl-4,4a,9,10-tetrahydro-2(3H)-phenanthrone

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Direct Synthesis of Ternary Iminium Salts by Combination of Aldehydes or Ketones with Secondary Amine Salts1,2

Cited by 148 publications

References 0 publications

Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes

Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes

Stereochemical Models for Discussing Additions to α,β‐Unsaturated Aldehydes Organocatalyzed by Diarylprolinol or Imidazolidinone Derivatives – Is There an ‘(E)/(Z)‐Dilemma’?

Photochemical studies on 4a-methyl-4,4a,9,10-tetrahydro-2(3H)-phenanthrone

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Direct Synthesis of Ternary Iminium Salts by Combination of Aldehydes or Ketones with Secondary Amine Salts^1,2