RSS-Feed abonnieren
Bitte kopieren Sie die angezeigte URL und fügen sie dann in Ihren RSS-Reader ein.
https://www.thieme-connect.de/rss/thieme/de/10.1055-s-00000083.xml
Synlett 2009(16): 2711-2712
DOI: 10.1055/s-0029-1218016
DOI: 10.1055/s-0029-1218016
SPOTLIGHT
© Georg Thieme Verlag
Stuttgart ˙ New York
The MgCl2-Et3N Base System: A Useful Reagent in Organic Synthesis
Weitere Informationen
Publikationsverlauf
Publikationsdatum:
14. September 2009 (online)
Biographical Sketches
Introduction
The combination of MgCl2 and Et3N is a considerably stronger base than Et3N alone. This base system has been used for a variety of base-induced reactions such as: α-carboxylation of ketones, [¹] condensation, [²] acylation of malonate derivatives, [³] [4] phosphonoacetes, [5] [6] anti-aldol [7] and imine aldol [8] reactions, ortho-formylation of phenols, [9] and Mannich reactions. [¹0] Moreover, this base system was used in Dieckman-type cyclizations [¹¹] and also for the preparation of β-ketoamides by the condensation of ketenes and isocyanates. [¹²]
Abstracts
(A) α-Carboxylation of ketones with carbon dioxide in the presence of MgCl2-Et3N followed by reaction with methyl vinyl ketone (MVK) yielded the Michael adducts in 42-75% yields or the Robinson adducts in 56-70% yields. This method reduced the polymerization of MVK usually observed under strong basic conditions. [¹] | |
(B) α,β-Unsaturated cyano esters were prepared by the condensation of aryl aldehydes with ethyl cyanoacetate in the presence of MgCl2-Et3N as catalyst. [²] | |
(C) Acylation of diethyl malonate with an acid chloride using MgCl2-Et3N as base gave adducts in excellent yields. This method was also used for the preparation of β-oxo esters from ethyl malonate mono potassium salt and acid chlorides in 92-99% yields. [³] | |
(D) Acylation of (acylamino)malonate with MgCl2-Et3N as base afforded α-acyl β-keto esters in good to excellent yields with a variety of acid chlorides. [4] | |
(E) Acylation of triethyl α-fluorophosphonoacetate with 2.2 equivalents of a benzoyl chloride in dry toluene and in the presence of MgCl2-Et3N afforded the diacylated adduct, which was deacylated in aqueous ethyl acetate and in the presence of SiO2 to α-fluoro-β-keto esters. Good to excellent yields (78-94%) were obtained. [5] | |
(F) Acylation of diethyl phosphonoacetic acid in the presence of MgCl2-Et3N as base gave β-keto phosphonates in 40-90% yields. [6] | |
(G) In 2002 Evans and co-workers used MgCl2-Et3N in anti-aldol reactions of chiral N-acyloxazolidinones in the presence of chlorotrimethylsilane. [7] The adducts were formed with high diastereoselectivity (dr up to 32:1). The reactions are operationally simple and can be run without rigorous exclusion of water. | |
(H) Stereoselective imine aldol reactions of N-cyclohexylimine with aromatic aldehydes in the presence of MgCl2-Et3N were reported recently by Hayashi et al. [8] High yields of products were obtained consisting essentially of the erythro isomer. | |
(I) A combination of MgCl2-Et3N was used as base in the ortho-formylation of phenols by Skattebøl and co-workers. [9] The reaction gave higher yields (70-99%) and fewer byproducts compared to most other methods. | |
(J) Phenols react with Eschenmoser’s salt in the presence of the MgCl2-Et3N as base, affording exclusively ortho-substituted benzylamines in high yields (66-98%). [¹0] |
- 1
Olsen RS.Fataftah ZA.Rathke MW. Synth. Commun. 1986, 16: 1133 - 2
Zhang M.Zhang A.-Q.Huang Y.-X. Youji Huaxue 2005, 25: 1133 -
3a
Rathke MW.Cowan PJ. J. Org. Chem. 1985, 50: 2622 -
3b
Rathke MW.Nowak MA. Synth. Commun. 1985, 15: 1039 -
3c
Kuo DL. Tetrahedron 1992, 48: 9233 -
3d
Clay RJ.Collom TA.Karrick GL.Wemple J. Synthesis 1993, 290 - 4
Krysan DJ. Tetrahedron Lett. 1996, 37: 3303 - 5
Kim DY.Lee YM.Choi YJ. Tetrahedron 1999, 55: 12983 - 6
Corbel B.L"Hostis-Kervella I.Haelters J.-P. Synth. Commun. 2000, 30: 609 -
7a
Evans DA.Tedrow JS.Shaw JT.Downey CW. J. Am. Chem. Soc. 2002, 124: 392 -
7b
Evans DA.Downey CW.Shaw JT.Tedrow JS. Org. Lett. 2002, 4: 1127 -
8a
Hayashi K.Kujime E.Katayama H.Sano S.Nagao Y. Chem. Pharm. Bull. 2007, 55: 1773 -
8b
Hayashi K.Kogiso H.Sano S.Nagao Y. Synlett 1996, 1203 -
9a
Hofsløkken NU.Skattebøl L. Acta Chem. Scand. 1999, 53: 258 -
9b
Hansen TV.Skattebøl L. Org. Synth. 2005, 82: 64 - 10
Anwar HF.Skattebøl L.Hansen TV. Tetrahedron 2007, 63: 9997 - 11
Tamai S.Ushirogochi H.Sano S.Nogao Y. Chem. Lett. 1995, 295 - 12
Lasley CL.Wright BB. Synth. Commun. 1989, 19: 59
References
- 1
Olsen RS.Fataftah ZA.Rathke MW. Synth. Commun. 1986, 16: 1133 - 2
Zhang M.Zhang A.-Q.Huang Y.-X. Youji Huaxue 2005, 25: 1133 -
3a
Rathke MW.Cowan PJ. J. Org. Chem. 1985, 50: 2622 -
3b
Rathke MW.Nowak MA. Synth. Commun. 1985, 15: 1039 -
3c
Kuo DL. Tetrahedron 1992, 48: 9233 -
3d
Clay RJ.Collom TA.Karrick GL.Wemple J. Synthesis 1993, 290 - 4
Krysan DJ. Tetrahedron Lett. 1996, 37: 3303 - 5
Kim DY.Lee YM.Choi YJ. Tetrahedron 1999, 55: 12983 - 6
Corbel B.L"Hostis-Kervella I.Haelters J.-P. Synth. Commun. 2000, 30: 609 -
7a
Evans DA.Tedrow JS.Shaw JT.Downey CW. J. Am. Chem. Soc. 2002, 124: 392 -
7b
Evans DA.Downey CW.Shaw JT.Tedrow JS. Org. Lett. 2002, 4: 1127 -
8a
Hayashi K.Kujime E.Katayama H.Sano S.Nagao Y. Chem. Pharm. Bull. 2007, 55: 1773 -
8b
Hayashi K.Kogiso H.Sano S.Nagao Y. Synlett 1996, 1203 -
9a
Hofsløkken NU.Skattebøl L. Acta Chem. Scand. 1999, 53: 258 -
9b
Hansen TV.Skattebøl L. Org. Synth. 2005, 82: 64 - 10
Anwar HF.Skattebøl L.Hansen TV. Tetrahedron 2007, 63: 9997 - 11
Tamai S.Ushirogochi H.Sano S.Nogao Y. Chem. Lett. 1995, 295 - 12
Lasley CL.Wright BB. Synth. Commun. 1989, 19: 59