10250-48-3Relevant academic research and scientific papers
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.
REACTIONS OF γ-ACYLOXY-β-KETOPHOSPHONATES: NEW ROUTES TO 3(2H)- AND 2(3H)-DIHYDROFURANONES
Drtina, Gary J.,Sampson, Paul,Wiemer, David F.
, p. 4467 - 4470 (1984)
Depending on the reaction conditions, γ-acyloxy-β-ketophosphonate anions can undergo either an intramolecular Wittig-like condensation or an unexpected rearrangement which affords an enol ester product.
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.
Novel Preparation of α,β-Unsaturated Aldehydes. Benzeneselenolate Promotes Elimination of HBr from α-Bromoacetals
Vasil'ev, Andrei,Engman, Lars
, p. 2151 - 2162 (2007/10/03)
Acetalization, α-bromination, nucleophilic phenylselenenylation, oxidative elimination/hydrolysis was investigated as a novel protocol for the α,β-dehydrogenation of aldehydes. Treatment of acetals with bromine in methylene chloride afforded the corresponding α-bromoacetals in 80-90% yields. Nucleophilic phenylselenenylation was then conveniently effected by treatment with benzenese-lenolate generated in situ in dimethyl sulfoxide from diphenyl diselenide, hydrazine and potassium carbonate. Unbranched α-bromoacetals cleanly afforded substitution products whereas β- and γ-branched ones gave substantial amounts of α,β-unsaturated acetals via formal loss of hydrogen bromide. Oxidative elimination/hydrolysis of these mixtures afforded α,β-unsaturated aldehydes in 50-80% overall yields. In the case of tertiary α-bromoacetals, treatment with benzeneselenolate afforded only dehydrobromination products as mixtures of isomers. The presence of at least a catalytic amount of the organoselenium reagent was found to be crucial for olefin formation. A SET-mechanism, involving benzeneselenolate-induced electron transfer to the halide, loss of bromide ion, and hydrogen atom or proton/electron was proposed for the benzenselenolate-promoted elimination reaction. Experiments designed to trap carbon-centered radicals in intramolecular cyclization or ring-opening reactions failed to provide any evidence for free-radical intermediates.
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.
Improved Synthesis of Tertiary Alkylacetic Acids and Esters
Randriamahefa, S.,Deschamps, P.,Gallo, R.,Grangette, H.
, p. 493 - 495 (2007/10/02)
Tertiary alkylacetic acids (R3CCH2COOH) are prepared by reaction of 1,1-dichloroethene with a reagent capable of forming readily a tertiary alkyl carbenium ion with sulfuric acid in the absence of boron trifluoride.With tertiary butyl reagents, the yields are good and the method is convenient at laboratory and larger scales.The yields of carboxylic acids fall sharply with increasing steric effects.The esters are obtained directly, by adding alcohols, in a one-pot synthesis; with C1-C3 alcohols the reaction is selective.
The Reactivity of Carbenes from Photolysis of Diazo-Compounds towards Carbon-Hydrogen Bonds. Effects of Structure, Temperature, and Matrix on the Insertion Selectivity
Tomioka, Hideo,Itoh, Masami,Yamakawa, Shyoji,Izawa, Yasuji
, p. 603 - 609 (2007/10/02)
Direct and/or sensitized photolyses of diazo-acetate (1a) and -malonate (1b) in hydrocarbons and ether were investigated at various temperatures in order to learn more about the nature of the C-H insertion process and the structural factors governing positional selectivity within the matrix.Photolysis of the diazo-compounds in a rigid matrix resulted in a marked decrease in the insertion selectivity, which may be interpreted as indicating that the matrix imposes severe steric demand especially on the direct C-H insertion process of the singlet carbene.The addition of a sensitizer in matrix photolysis causes a marked increase in the selectivity in the case of (1a), as is observed in the comparable liquid-phase experiment, but it causes a decrease in the case of (1b).This is interpreted as suggesting that the excited triplet (1b) itself is involved in C-H insertion under these conditions.More extensive temperature studies show that, as the temperature decreases, the C-H insertion selectivity of :CHCO2R decreases regularly regardless of the reaction phase, whereas that of :C(CO2R)2 increases in the liquid phase but decreases in the solid phase.This difference in the temperature dependence is explained by assuming that the singlet carbene is responsible for the C-H insertion of :CHCO2R throughout the temperature range studied, while both singlet and triplet are involved in the insertion of :C(CO2R)2.
Mechanism of the Photochemical Wolff Rearrangement. The Role of Conformation in the Photolysis of α-Diazo Carbonyl Compounds.
Tomioka, Hideo,Okuno, Hiroshi,Izawa, Yasuji
, p. 5278 - 5283 (2007/10/02)
Investigation of photochemical processes of several α-diazo carbonyl compounds reveals that the Wolff rearrangement to form ketene takes place directly from the singlet excited state of the s-Z conformer whereas the excited state of the s-E conformer dissociates nitrogen to generate singlet carbonyl carbene, which either undergoes characteristic carbenic reactions, e.g., insertion and 1,2-hydrogen shift, or gives rise to ketene.The migratory aptitude as well as the relative efficiency of other competing reactions from singlet carbene is shown to be an important factor in dete rmining which reaction pathway is favored.Substantial amounts of singlet carbene can be formed even under sensitized conditions, presumably via intersystem crossing from initially formed triplet carbene.
