10250-48-3Relevant articles and documents
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Doering,W. von E.,Knox,L.H.
, p. 1989 - 1992 (1961)
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ALKYLATION DE QUELQUES COMPOSES CARBONYLES PAR DES GROUPES TERTIAIRES. UTILISATION DE LA REACTION DE FRIEDEL-CRAFTS DANS LA SYNTHESE D'ESTERS ET DE CETONES ENCOMBRES
Lion, Claude,Dubois, Jacques-Emile
, p. 319 - 323 (1981)
t-Alkylation of carboxylic esters via their ketene alkyl trimethylsilyl acetels by the Friedel-Crafts reaction allows the synthesis of new higly hindered compounds.A new route using sodium amide in dimethoxyethane, for the preparation of trimethylsilyl enol ethers of ketones, is described.The α-butylation of these compounds permits the synthesis of new crowded pentasubstituted ketones.The limits as well as the performance of the method have been studied.
Flash vacuum pyrolysis of tert-butyl β-ketoesters: Sterically protected α-oxoketenes
Leung-Toung,Wentrup
, p. 7641 - 7654 (1992)
Infrared spectroscopic analysis of the products showed that flash vacuum pyrolyses (FVP) of dimethyl tert-butylmalonate (1b) and methyl tert-butyl(pivaloyl)acetate (1d) at ca. 550°C afforded the corresponding tert-butyl(carbomethoxy)ketene (4b) and tert-butyl(pivaloyl)ketene (4d), respectively, with loss of methanol, together with unreacted 1b and 1d (Ar matrix, 12 K or neat at 77 K; 10-5 mbar). Monitoring by IR spectroscopy showed that 4b reacted with methanol at ca. -50°C to give 1b. Ketene 4d does not react with methanol at room temperature, but afforded ester 1d on refluxing for 8 h. FVP of 1b and 1d at temperatures above 650°C gave the α-oxoketenes 4b and 4d, respectively, unsubstituted dimethyl malonate (1a) and methyl 4,4-dimethyl-3-oxo-pentanoate (1c), respectively, due to retro-ene reactions with elimination of isobutene, as well as pyrolysis products derived from 1a and 1c, respectively. FVP of α-unsubstituted β-ketoesters 1a and 1c at ca. 500°C (10-5 mbar) with argon matrix isolation of the products at 12 K afforded the ketenes 4a and 4c as mixtures of s-Z and s-E conformers together with mixtures of unreacted keto (1a, c) and enol forms (2a, c). On warming to temperatures between -90 and -50°C, back-reaction of ketenes 4a, c with methanol resulted in the re-generation of enols 2a, c without increasing the amounts of the keto forms 1a, c.
Synthesis, stereochemistry, and photochemical and thermal behaviour of bis-tert-butyl substituted overcrowded alkenes
Ter Wiel, Matthijs K. J.,Kwit, Marcin G.,Meetsma, Auke,Feringa, Ben L.
, p. 87 - 96 (2008/03/14)
In order to study the structural limits in the design of molecular motors, a tert-butyl substituted analogue was prepared. The unexpected photochemical and thermal isomerisation processes and the stereochemistry of new overcrowded alkene 5 are described. The bis tert-butyl substituted alkenes were synthesised in a five-step sequence with an overall yield of 7.5%. Structural assignments of the isomers based on experimental data were supported by calculations of all four isomers of the alkene. X-Ray crystal analysis showed a strongly twisted alkene (torsion angle 39°) for a less stable photochemically generated cis-isomer. The Royal Society of Chemistry.
E/Z Isomerization, Solvolysis, Addition, and Cycloaddition Reactions of (E)-tert-Butylketene Methyl tert-Butyldimethylsilyl Acetal
Adam, Waldemar,Wang, Xiaoheng
, p. 7244 - 7250 (2007/10/02)
In the presence of catalytic amounts of CF3COCH3 or CF3COCF3, the silyl ketene acetal E-1 was isomerized into its Z isomer (Z/E ratio 90:10).For this novel E/Z isomerization a mechanism is proposed, in which addition and reelimination of the fluoro ketone, through a 1,4-dipolar intermediate operates.With the protic nucleophiles CH3OH, CF3CH2OH, or PhOH, the ketene acetal E-1 afforded the ortho esters 2 as addition products, while CH3CO2H, CF3CO2H, or H2O led to methyl pivalate as the solvolysis product.This chemistry is readily explained through protonation of the ketene acetal E-1 to generate the corresponding carbenium ion.At low temperature the reaction with TCNE gave the silylketene imine 3 as labile cycloadduct, which underwent on workup desilylation to give the TCNE-incorporated ester 6; the latter eliminated hydrogen cyanide at room temperature to give the ene ester 7.With MTAD the labile silyl ene product 4 was obtained initially, which underwent silyl migration to give N-silylated urazole 8; final desilylation led to the stable urazole 9.Also for the ene reactions of TCNE and MTAD with the silyl ketene acetal E-1, a 1,4-dipolar intermediate is proposed to intervene.
