Condensare Dieckmann

Condensarea Dieckmann este o reacție organică de de condensare intramoleculară a diesterilor, în mediu bazic, cu obținerea de β-ceto esteri.[1][2][3][4][5] A fost denumită după chimistul german Walter Dieckmann (1869–1925). Versiunea intermoleculară a acestei reacții este condensarea Claisen.

Condensarea Dieckmann
Condensarea Dieckmann

Printre altele, condensările Dieckmann pot fi folosite pentru obținerea de cicloalcani și de derivați ai acestora, printr-o succesiune de etape.

Mecanism

Prin deprotonarea unui ester în poziția α se obține un ion enolat, la care are loc un atac nucleofil. Se obține un enol ciclic care, prin protonare cu un acid Brønsted (H3O+ de exemplu) reface β-ceto esterul.[6]

Mecanismul condensării Dieckmann
Mecanismul condensării Dieckmann

Datorită stabilității sterice a ciclurilor penta- și hexaciclice, aceste structuri vor fi favorizate și se vor forma mai ușor. 1,6-diesterii vor forma β-ceto esteri pentaciclici, iar 1,7-diesterii vor forma β-ceto esteri hexaciclici.[7]

Animation zum Reaktionsmechanismus der Dieckmann-Kondensation
Animație a mecanismului de reacție.

Vezi și

Referințe

  1. ^ Dieckmann, W. Ber. 1894, 27, 102 & 965
  2. ^ Dieckmann, W. Ber. 1900, 33, 595 & 2670
  3. ^ Dieckmann, W. Ann. 1901, 317, 51 & 93
  4. ^ Schaefer, J. P.; Bloomfield, J. J. (). „The Dieckmann Condensation (Including the Thorpe-Ziegler Condensation)”. Organic Reactions. 15: 1–203. doi:10.1002/0471264180.or015.01. 
  5. ^ Davis, B. R.; Garrett, P. J. Comp. Org. Syn. 1991, 2, 806-829. (Review)
  6. ^ Janice Gorzynski Smith (). Organic Chemistry (ed. 2nd). pp. 932–933. ISBN 978-0073327495. 
  7. ^ „Dieckmann Condensation”. Organic Chemistry Portal. 

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