Intramolecular Dehydration of Dialkylacetic Acids and Trimethylsilylacetic Acid with Dicyclohexylcarbodiimide to the Corresponding Stable Ketenes
A new, simple preparation for stable dialkyl ketenes involving intramolecular dehydration of appropriately substituted acetic acids with dicyclohexylcarbodiimide (DCC) in the presence of catalytic amounts of triethylamine gives 60-70percent yield of the corresponding ketenes.Trimethylsilylacetic acid also gives trimethylsilylketene in good yield.
A high yielding, reproducible synthesis of trimethylsilylketene
A two-step sequence for the preparation of trimethylsilylketene, from chloroacetaldehyde diethyl acetal via ethoxyacetylene, has been modified and optimized.
Black, T. Howard,Farrell, John R.,Probst, Donald A.,Zotz, Michael C.
Chiral dirhodium(II) carboxamidate-catalyzed [2 + 2]-cycloaddition of TMS-ketene and ethyl glyoxylate
The [2 + 2]-cycloaddition reaction between ethyl glyoxylate and trimethylsilylketene is reported. Enantiomeric excesses up to 83% have been achieved with the use of only 1.0 mol % of a previously unreported chiral imidazolidinone-ligated dirhodium(II) carboxamidate catalyst. An extensive survey of chiral catalysts has shown that enantiocontrol for cycloaddition increases as the steric bulk of the ligand is increased. However, enantioselectivity is increased to 99% ee by the addition of 10 mol % of quinine as a co-catalyst with a chiral dirhodium(II) azetidinone-ligated catalyst, and there is a significant decrease in reaction time.
Forslund, Raymond E.,Cain, James,Colyer, John,Doyle, Michael P.
p. 87 - 92
(2007/10/03)
The formation of silylated β-lactams from silylketenes through Lewis acid promoted [2+2] cycloaddition: A combined theoretical and experimental study
The stereoselective formation of silylated cis-β-lactams from (trimethylsilyl)ketene and an α-imino ester by Lewis acid catalysis is described. Theoretical results suggest that the reaction between (trimethylsilyl)ketene and trans- (methoxycarbonyl)-N-methylformaldimine would proceed most favourably with the BF3 catalyst coordinated to the ketene. Moreover, the calculated energy barriers account for the cis:trans ratio found experimentally. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).
Pelotier, Beatrice,Rajzmann, Michel,Pons, Jean-Marc,Campomanes, Pablo,Lopez, Ramon,Sordo, Tomas L.
p. 2599 - 2606
(2007/10/03)
C2-Symmetric Cu(II) Complexes as Chiral Lewis Acids. Catalytic, Enantioselective Cycloadditions of Silyl Ketenes
(matrix presented) C2-Symmetric bis(oxazoline)-Cu(II) complexes (4a-g) catalyze the enantioselective [2 + 2] cycloaddition between (silyl)ketenes and chelating carbonyl substrates. A range of substituted β-lactones can be produced in excellent yields and selectivities. It was also found that (trimethylsilyl)-ketene (1) may also undergo a highly selective hetero Diels-Alder reaction with β,γ-unsaturated α-keto esters.
Evans, David A.,Janey, Jacob M.
p. 2125 - 2128
(2007/10/03)
Convenient Synthesis of Silylketenes from 1-tert-Butoxy-2-silylethynes
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Valenti, Eduard,Pericas, Miquel A.,Serratosa, Felix
p. 395 - 397
(2007/10/02)
Silylierungsreaktionen an Ketenderivaten
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Uhlig, Wolfram,Tzschach, Alfred
p. 409 - 410
(2007/10/02)
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