Regioselective Enamine Formation from Oxonia‐Boranuida‐Betaines and Their Application in Asymmetric Michael Reactions

Christoffers, Jens; Kreidler, Burkard; Unger, Sven; Frey, Wolfgang

doi:10.1002/ejoc.200300191

Cited by 37 publications

(23 citation statements)

References 41 publications

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“…Enaminones have been studied not only as ligands in coordination chemistry [2], but also as chiral auxiliaries in organic synthesis [3]. In continuation of investigation of the chemistry of organometallic enaminones, the title compound, as an intermediate, has been synthesized via the Claisen condensation of acetylferrocene and dimethyl isophthalate [4,5].…”

Section: Discussionmentioning

confidence: 99%

Crystal structure of 1,3-benzene-bis(1-ferrocenyl-3-hydroxyprop-2-en-1-one), (C5H5)Fe(C22H16O4)Fe(C5H5)

Shi

Cheng

Zhou

et al. 2006

Zeitschrift Für Kristallographie - New Crystal Structures

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Source of materialAcetylferrocene was obtained from the reaction of ferrocene and acetic anhydride as described previously [1]. A solution of sodium ethoxide (5.036 g, 74 mmol), acetylferrocene (16.877 g, 74 mmol) and dimethyl isophthalate (7.157 g, 37 mmol) in 60 ml THF was refluxed under nitrogen for 3 h. The yellow solid was filtered, washed with THF, then dissolved in hot water and finally acidified with aqueous acetic acid to afford the title compound (8.032 g, yield 37 %) as dark red solid. Recrystallization from dichloromethane and hexane gave crystals suitable for X-ray analysis (m.p. 184.5-185.7°C). DiscussionEnaminones have been studied not only as ligands in coordination chemistry [2], but also as chiral auxiliaries in organic synthesis [3]. In continuation of investigation of the chemistry of organometallic enaminones, the title compound, as an intermediate, has been synthesized via the Claisen condensation of acetylferrocene and dimethyl isophthalate [4,5]. 1 H NMR spectroscopy shows that the compound exists in the enol, and not in the keto form in solution. Interestingly, IR spectroscopy displays only the enol form in the solid state, this fact has been fully confirmed by the crystal structure (figure, top). As also noted for the related structure of (Z)-1-ferrocenyl-3-hydroxy-3-(2-pyridyl)-prop-2-en-1-one [6], the O=CC=CO fragments are planar. The bond lengths indicate electron delocalization [7]. Two O=CC=CO planes are twisted with respect to the benzene ring (C6 C10) and the substituted cyclopentadienyl ring (C23 C27) by 26.0(3)°, 7.2(3)°and 22.9(3)°, 9.3 (3)°, respectively. The two cyclopentadienyl rings in the ferrocenyl group are almost parallel (dihedral angles are 2.1(4)°for the first ferrocenyl group and 2.9(4)°for the second one) and adopt a different conformation, viz. eclipsed for the first ferrocenyl group and staggered for the second. Furthermore, two ferrocenyl groups are cis with respect to the benzene ring. The C13C14 and C18C20 bonds of 1.481(7) Å and 1.484(7) Å, respectively, which are typical of a single C sp2Csp2 bond, suggest that the benzene ring is not involved in the conjugation of the O=CC=CO groups. In addition to the intramolecular hydrogen bonds (OH···O=C), intermolecular hydrogen bond (CH···O=C) is also present in the crystal structure of the title compound ( figure, bottom).

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Section: Discussionmentioning

confidence: 99%

Crystal structure of 1,3-benzene-bis(1-ferrocenyl-3-hydroxyprop-2-en-1-one), (C5H5)Fe(C22H16O4)Fe(C5H5)

Shi

Cheng

Zhou

et al. 2006

Zeitschrift Für Kristallographie - New Crystal Structures

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“…Stabilization of the enaminone form, in Schiff base enaminone equilibrium (Scheme 1), of other organic compounds is well described in the literature [2,3]. Besides, the application of enamines in enantioselective C-C bond forming reactions is also reported [4,5].…”

Section: Introductionmentioning

confidence: 91%

X-Ray and EPR study on copper (II) complexes with an enamine ligand

Ahmedova

Vaz²,

Ciattini

et al. 2005

Open Chemistry

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The enamine (HEAID) obtained from aniline and 2-acetyl-1,3-indandione (2AID) behaves as a bidentate ligand in coordination with copper(II) ion. Two types of crystals, apparently different in shape, were isolated and studied by single-crystal X-ray diffraction. The X-ray data for the brown rhombic crystals of compound 1 shows a mononuclear complex of Cu(II) coordinated with two EAID − anions, Cu(EAID) 2 . The X-ray data for the green crystals of compound 2 shows a dinuclear Cu(II) complex with two OH − groups acting as bridging ligands, [Cu 2 (µ-OH) 2 (EAID) 2 ]. In both cases the ligand coordinates after deprotonation of the amine group.

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“…42 Although interesting ee's have been realized, the preparation of such chiral enamides is more difficult than that of the compounds 47. A different approach has been adopted by Jørgensen and his co-workers.…”

Section: Group X Palladium and Platinum (mentioning

confidence: 99%

Michael additions catalyzed by transition metals and lanthanides species. A review. Part 1. Transition metals

Comelles¹,

Moreno‐Mañas²,

Vallribera³

2005

Arkivoc

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Regioselective Enamine Formation from Oxonia‐Boranuida‐Betaines and Their Application in Asymmetric Michael Reactions

Cited by 37 publications

References 41 publications

Crystal structure of 1,3-benzene-bis(1-ferrocenyl-3-hydroxyprop-2-en-1-one), (C5H5)Fe(C22H16O4)Fe(C5H5)

Crystal structure of 1,3-benzene-bis(1-ferrocenyl-3-hydroxyprop-2-en-1-one), (C5H5)Fe(C22H16O4)Fe(C5H5)

X-Ray and EPR study on copper (II) complexes with an enamine ligand

Michael additions catalyzed by transition metals and lanthanides species. A review. Part 1. Transition metals

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