Seyferthova–Gilbertova homologace

Seyferthova–Gilbertova homologace je reakce arylového ketonu 1 (nebo aldehydu) s dimethyl(diazomethyl)fosfonátem 2 a terc-butoxidem draselným za vzniku substituovaného alkynu 3.[1][2]

Dimethyl(diazomethyl)fosfonáty 2 bývají občas nazývány Seyferthova–Gilbertova činidla.[3]

Znázornění Seyferthovy–Gilbertovy homologace
Znázornění Seyferthovy–Gilbertovy homologace

Tato reakce patří mezi homologace, protože její produkt obsahuje o jeden atom uhlíku více než původní reaktant.

Mechanismus

Deprotonací Seyferthova–Gilbertova činidla A vzniká anion B, který reaguje s ketonem za tvorby oxafosfetanu D. Eliminací dimethylfosfátu E se vytvoří vinyldiazo meziprodukt s rezonančními strukturami Fa a Fb. Po vzniku plynného dusíku vznikne vinylkarben G, jenž se 1,2-přesmykem změní na alkyn H.

Mechanismus Seyferthovy–Gilbertovy homologace
Mechanismus Seyferthovy–Gilbertovy homologace

Bestmannova varianta

Ohirovo–Bestmannovo činidlo
Strukturní vzorec
Strukturní vzorec
Obecné
Systematický názevdimethyl(1-diazo-2-oxopropyl)fosfonát
Sumární vzorecC5H9N2O4P
Identifikace
Registrační číslo CAS90965-06-3
PubChem11106189
SMILESO=P(OC)(OC)C(C(C)=O)=[N+]=[N-]
InChIInChI=1/C5H9N2O4P/c1-4(8)5(7-6)12(9,10-2)11-3/h1-3H3
Vlastnosti
Molární hmotnost192,11 g/mol
Není-li uvedeno jinak, jsou použity
jednotky SI a STP (25 °C, 100 kPa).

Některá data mohou pocházet z datové položky.

Dimethyl(diazomethylfosfonátový karboanion lze získat reakcí dimethyl-1-diazo-2-oxopropylfosfonátu, také nazývaného Ohirovo-Bestmannovo činidlo) s methanolem a uhličitanem draselným (sloužícím jako zásada), při kterém dojde k odštěpení acetylové skupiny v podobě methylacetátu. Reakcemi Bestmannova činidla s aldehydy vznikají koncové alkyny, často s velmi vysokými výtěžnostmi, v méně krocích než v Coreyově–Fuchsově reakci.[4][5]

Bestmannovo činidlo
Bestmannovo činidlo

Použití uhličitanu draselného umožňuje zapojit do této reakce širší rozmezí funkčních skupin.

Upravená in situ příprava Ohirova-Bestmannova činidla

Bezpečná příprava alkynů z aldehydů

Byl vyvinut bezpečnější a lépe laditelný postup přípravy alkynů z aldehydů. Jeho výhodami jsou použití stabilního sulfonylazidu, místo tosylazidu, k získání Ohirova−Bestmannova činidla.[6]

Ostatní obměny

U méně reaktivních aldehydů lze uhličitan draselný nahradit uhličitanem cesným a methanolem, čímž se výrazně navýší výtěžnost.[7]

Odkazy

Související články

Externí odkazy

Reference

V tomto článku byl použit překlad textu z článku Seyferth–Gilbert homologation na anglické Wikipedii.

  1. D. Seyferth; R. S. Marmor. Reactions of dimethylphosphono-substituted diazoalkanes. (MeO)2P(O)CR transfer to olefins and 1,3-dipolar additions of (MeO)2P(O)C(N2)R. The Journal of Organic Chemistry. 1971, s. 1379–1386. DOI 10.1021/jo00809a014. 
  2. J. C. Gilbert; U. Weerasooriya. Diazoethenes: their attempted synthesis from aldehydes and aromatic ketones by way of the Horner-Emmons modification of the Wittig reaction. A facile synthesis of alkynes. The Journal of Organic Chemistry. 1982, s. 1837–1845. DOI 10.1021/jo00349a007. 
  3. D. G. Brown; E. J. Velthuisen; J. R. Commerford; R. G. Brisbois; T. H. Hoye. A Convenient Synthesis of Dimethyl (Diazomethyl)phosphonate (Seyferth/Gilbert Reagent). The Journal of Organic Chemistry. 1996, s. 2540–2541. DOI 10.1021/jo951944n. 
  4. S. Müller; B. Liepold; G. Roth; H. J. Bestmann. An Improved One-pot Procedure for the Synthesis of Alkynes from Aldehydes. Synlett. 1996, s. 521–522. DOI 10.1055/s-1996-5474. 
  5. G. Roth; B. Liepold; S. Müller; H. J. Bestmann. Further Improvements of the Synthesis of Alkynes from Aldehydes. Synthesis. 2004, s. 59–62. DOI 10.1055/s-2003-44346. 
  6. Jepsen, T.H, Kristensen, J.L. J. Org. Chem. 2014, "In Situ Generation of the Ohira–Bestmann Reagent from Stable Sulfonyl Azide: Scalable Synthesis of Alkynes from Aldehydes". http://pubs.acs.org/doi/abs/10.1021/jo501803f
  7. Lidija Bondarenko; Ina Dix. Cyclophanes. Part LII:1 Ethynyl[2.2]paracyclophanes – New Building Blocks for Molecular Scaffolding. Synthesis. 2004, s. 2751–2759. DOI 10.1055/s-2004-834872. 

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