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Volumn 73, Issue 6, 2008, Pages 2033-2040

Scope of the asymmetric intramolecular stetter reaction catalyzed by chiral nucleophilic triazolinylidene carbenes

Author keywords

[No Author keywords available]

Indexed keywords

AMIDES; CATALYSIS; ENANTIOSELECTIVITY; REACTION KINETICS; SULFUR;

EID: 41849101072     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo702313f     Document Type: Article
Times cited : (138)

References (57)
  • 6
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    • For recent examples of an asymmetric benzoin reaction, see: a
    • For recent examples of an asymmetric benzoin reaction, see: (a) Knight, R. L.; Leeper, F. J. J. Chem. Soc., Perkin Trans. 1 1998, 1891-1893.
    • (1998) J. Chem. Soc., Perkin Trans. 1 , pp. 1891-1893
    • Knight, R.L.1    Leeper, F.J.2
  • 8
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    • An intramolecular crossed-benzoin reaction has been demonstrated; see: (c) Enders, D, Niemeier, O, Balensiefer, T. Angew. Chem, Int. Ed. 2006, 45, 1463-1467
    • An intramolecular crossed-benzoin reaction has been demonstrated; see: (c) Enders, D.; Niemeier, O.; Balensiefer, T. Angew. Chem., Int. Ed. 2006, 45, 1463-1467.
  • 10
    • 1642295713 scopus 로고    scopus 로고
    • For an elegant solution to the intermolecular cross-benzoin chemoselectivity problem, see: e
    • For an elegant solution to the intermolecular cross-benzoin chemoselectivity problem, see: (e) Linghu, X.; Potnick, J. R.; Johnson, J. S. J. Am. Chem. Soc. 2004, 126, 3070-3071.
    • (2004) J. Am. Chem. Soc , vol.126 , pp. 3070-3071
    • Linghu, X.1    Potnick, J.R.2    Johnson, J.S.3
  • 14
    • 0000011522 scopus 로고    scopus 로고
    • Jacobsen, E. N, Pfaltz, A, Yamamoto, H, Ed, Springer: New York
    • (a) Enders, D.; Breuer, K. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Ed.; Springer: New York, 1999; Vol. 3, pp 1093-1102.
    • (1999) Comprehensive Asymmetric Catalysis , vol.3 , pp. 1093-1102
    • Enders, D.1    Breuer, K.2
  • 23
    • 1542375011 scopus 로고    scopus 로고
    • For related examples of acyl silanes in the Stetter reaction, see: a
    • For related examples of acyl silanes in the Stetter reaction, see: (a) Mattson, A. E.; Bharadwaj, A. R.; Scheidt, K. A. J. Am. Chem. Soc. 2004, 126, 2314-2315.
    • (2004) J. Am. Chem. Soc , vol.126 , pp. 2314-2315
    • Mattson, A.E.1    Bharadwaj, A.R.2    Scheidt, K.A.3
  • 27
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    • Reference 5
    • (a) Reference 5.
  • 35
    • 41849110894 scopus 로고    scopus 로고
    • We have shown that benzofuranones lacking the methine proton may be formed in extremely high enantiomeric excesses 99% ee, this product epimerizes slowly upon prolonged exposure to DBU suggesting that phenoxide elimination/conjugate addition is a viable pathway for racemization; see ref14b,f
    • We have shown that benzofuranones lacking the methine proton may be formed in extremely high enantiomeric excesses (99% ee); this product epimerizes slowly upon prolonged exposure to DBU suggesting that phenoxide elimination/conjugate addition is a viable pathway for racemization; see ref14b,f.
  • 36
    • 41849092138 scopus 로고    scopus 로고
    • Optically enriched product 35 was resubjected to an intramolecular Stetter reaction with 20 mol % triazolium salt 6, 20 mol % KHMDS for 24 h and was reisolated as the racemate.
    • Optically enriched product 35 was resubjected to an intramolecular Stetter reaction with 20 mol % triazolium salt 6, 20 mol % KHMDS for 24 h and was reisolated as the racemate.
  • 37
    • 41849115181 scopus 로고    scopus 로고
    • Reactions that contain an EWG on the aromatic backbone typically proceed to completion in 15-60 min. If the reaction is allowed to stir for 24 h, the product is isolated with enantiomeric excess between 67-80%. In addition, we briefly examined if erosion occurs during purification by column chromatography. Optically enriched 35 was dissolved in toluene and stirred with silica gel and the enantioselectivity decreased from 90% to 66% ee. Erosion of enantioselectivity could be avoided by treating the silica gel with 15% acetic acid prior to column chromatography.
    • Reactions that contain an EWG on the aromatic backbone typically proceed to completion in 15-60 min. If the reaction is allowed to stir for 24 h, the product is isolated with enantiomeric excess between 67-80%. In addition, we briefly examined if erosion occurs during purification by column chromatography. Optically enriched 35 was dissolved in toluene and stirred with silica gel and the enantioselectivity decreased from 90% to 66% ee. Erosion of enantioselectivity could be avoided by treating the silica gel with 15% acetic acid prior to column chromatography.
  • 41
    • 41849099551 scopus 로고    scopus 로고
    • One can ascribe the cause of this decomposition to both water and molecular oxygen. However, we hypothesize that in this particular experiment, oxygen is the real culprit, partly due to Colorado's arid climate and therefore a lower concentration of moisture, and partly to our subsequent observations involving the beneficial effects of argon bubbling through the solution.
    • One can ascribe the cause of this decomposition to both water and molecular oxygen. However, we hypothesize that in this particular experiment, oxygen is the real culprit, partly due to Colorado's arid climate and therefore a lower concentration of moisture, and partly to our subsequent observations involving the beneficial effects of argon bubbling through the solution.
  • 42
    • 41849127760 scopus 로고    scopus 로고
    • Decomposition products derived from the triazolinylidene carbene have so far resisted efforts directed towards their isolation and conclusive identification. Addition of water to the free carbene in an NMR tube generates a spectrum consistent with an aminal, the product of net water addition to the carbene carbon
    • Decomposition products derived from the triazolinylidene carbene have so far resisted efforts directed towards their isolation and conclusive identification. Addition of water to the free carbene in an NMR tube generates a spectrum consistent with an aminal, the product of net water addition to the carbene carbon.
  • 43
    • 33748954621 scopus 로고    scopus 로고
    • Enders has illustrated that triazolinylidene carbenes react with molecular oxygen, forming cyclic ureas: see: a
    • Enders has illustrated that triazolinylidene carbenes react with molecular oxygen, forming cyclic ureas: see: (a) Enders, D.; Breuer, K.; Runsink, J.; Teles, J. H. Liebigs Ann. Chem. 1996, 2019-2028.
    • (1996) Liebigs Ann. Chem , pp. 2019-2028
    • Enders, D.1    Breuer, K.2    Runsink, J.3    Teles, J.H.4
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    • Mechanism of the thiamine-catalyzed benzoin condensation reaction: (a) Breslow, R
    • Mechanism of the thiamine-catalyzed benzoin condensation reaction: (a) Breslow, R. J. Am. Chem. Soc. 1958, 80, 3719-3726.
    • (1958) J. Am. Chem. Soc , vol.80 , pp. 3719-3726
  • 48
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    • Mechanism of the cyanide-catalyzed reaction: (d) Lapworth, A
    • Mechanism of the cyanide-catalyzed reaction: (d) Lapworth, A. J. Chem. Soc. 1903, 83, 995-1005.
    • (1903) J. Chem. Soc , vol.83 , pp. 995-1005
  • 49
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    • do Amaral, L.; Bull, H. G.; Cordes, E. H. J. Am. Chem. Soc. 1972, 94, 7579-7580.
    • (e) do Amaral, L.; Bull, H. G.; Cordes, E. H. J. Am. Chem. Soc. 1972, 94, 7579-7580.
  • 50
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    • For the mechanism of the cyanide-catalyzed crossed silyl benzoin reactions, see: f
    • For the mechanism of the cyanide-catalyzed crossed silyl benzoin reactions, see: (f) Linghu, X.; Bausch. C. C.; Johnson, J. S. J. Am. Chem. Soc. 2005, 127, 1833-1840.
    • (2005) J. Am. Chem. Soc , vol.127 , pp. 1833-1840
    • Linghu, X.1    Bausch, C.C.2    Johnson, J.S.3
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    • See ref 4b
    • (a) See ref 4b.
  • 54
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    • Our original assignment for the absolute stereochemistry of 17 was based on the assumption that the aliphatic series was analogous to the aromatic series see ref 14a, This has since proved incorrect. The correct absolute chemistry is assigned by comparison to ref 26b
    • Our original assignment for the absolute stereochemistry of 17 was based on the assumption that the aliphatic series was analogous to the aromatic series (see ref 14a). This has since proved incorrect. The correct absolute chemistry is assigned by comparison to ref 26b.
  • 56
    • 41849090355 scopus 로고    scopus 로고
    • The proposed transition state is further supported by a recent example by Enders and co-workers utilizing chiral triazolium salts in an asymmetric intramolecular crossed-benzoin reaction. See ref 2c
    • The proposed transition state is further supported by a recent example by Enders and co-workers utilizing chiral triazolium salts in an asymmetric intramolecular crossed-benzoin reaction. See ref 2c.
  • 57
    • 41849100653 scopus 로고    scopus 로고
    • This model is an MM2 minimization (Chem 3D) of the catalyst framework and substrate, followed by simple manipulation of the substituents within that software, and is meant to serve as a mnemonic rather than a transition state approximation. We are currently engaged in a collaboration to provide theoretical and computational support for this model
    • This model is an MM2 minimization (Chem 3D) of the catalyst framework and substrate, followed by simple manipulation of the substituents within that software, and is meant to serve as a mnemonic rather than a transition state approximation. We are currently engaged in a collaboration to provide theoretical and computational support for this model.


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