41785-81-3Relevant academic research and scientific papers
Ultrasound-Assisted Preparation of Di-tert-Butyl-, Di-1,1'-Adamantyl- and (1-Adamantyl)-tert-Butylketenes
Olah, George A.,Wu, An-hsiang,Farooq, Omar
, p. 566 - 567 (1989)
Di-tert-butyl-, di(1-adamantyl)-, and (1-adamantyl)-tert-butylketenes were prepared in excellent yield from their corresponding acetyl chlorides with triethylamine under ultrasonic irradiation, showing a dramatic improvement over attempted conventional dehydrochlorination.
Acylation mechanisms of DMSO/[D6]DMSO with Di-tert-butylketene and its congeners
Knorr, Rudolf
experimental part, p. 6335 - 6342 (2011/12/05)
Dimethyl sulfoxide (DMSO) and tBu2C=C=O in diglyme require heating to about 150 °C to furnish the Pummerer-type product tBu 2CHCO2CH2SCH3 through a novel mechanistic variant. The "ester enolate" tBu2C=C(O -)-O-S+(CH3)2 arising through the reversible addition of DMSO (step 1) to C-1 of tBu2C=C=O must be trapped through protonation (step 2) at C-2 by a carboxylic acid catalyst to form tBu2CH-C(=O)-O-S+(CH3)2 so that the reaction can proceed. The ensuing cleavage (step 3) of the O-S bond and one of the C-H bonds in the-S(CH3)2 group (E2 elimination, no ylide intermediate) results in the formation of tBu2CHCO 2- and H3CS-CH2+, whose combination (step 4) generates the final product. With a mixture of DMSO and [D6]DMSO competing for tBu2C=C=O in diglyme, the small value of the kinetic H/D isotope effect (KIE) kH/kD = 1.26 at 150 °C indicates that the cleavage of the C-H/C-D bonds (step 3) does not occur in the transition state with the highest free enthalpy. Therefore, the practically isotope-independent steps 1 and 2 determine the overall rate. The alternative slow initial protonation at C-2 of tBu2C=C=O generating the acylium cation tBu2CHC≡O+ can be excluded. Preparatory studies were undertaken to compare the mechanistic behavior of tBu2C=C=O with that of two related acylating agents: (i) The anhydride (tBu2CHCO)2O affords the same Pummerer-type product more slowly, again with an unexpectedly small KIE of 1.24 at 150 °C, which indicates that the overall rate is limited here by the almost isotope-independent initial O-acylation of DMSO in the addition/elimination (AE) mechanism. (ii) The acyl chloride tBu2CHCOCl affords ClCH 2SCH3 through a more common mechanistic variant involving neither the ketene nor the acylium cation tBu2CHC≡O +: The modestly enhanced kH/kD value of 2.4 at 55 °C shows that the C-H/C-D bond fissions contribute to the overall rate in cooperation with the retarded initial O-acylation. Deuterium labeling was quantified through 1H and 13C NMR integrations of deuterium-shifted signals.
Shorter and easier syntheses of Di-tert-butylketene and related gem-Di-tert-butyl compounds
Knorr, Rudolf,Hennig, Karsten-Olaf,Schubert, Bernhard,Boehrer, Petra
experimental part, p. 6651 - 6664 (2011/02/26)
The ketene tBu2C=C=O is prepared from tBu2C=O in three steps (performable as a two-stage operation) through elimination of HCl from the intermediate product tBu2CCl-CH=O. The acid tBu 2CH-CO2H, obtainable in two, three, or four preparative stages from tBu2C=O, adds slowly to the ketene to produce the anhydride (tBu2CH-CO)2O. Elemental lithium together with ClSiMe3 converts tBu2CCl-CH=O into tBu2C=CH- OSiMe3, which is a durable precursor of tBu2CH-CH=O, making this aldehyde easily and cheaply available from tBu2C=O. By exclusion of alternative mechanistic possibilities, the reduction of tBu 2CCl-CH=O by tBuMgCl is shown to involve at least one single-electron transfer, leading to the enolate tBu2C=CH-OMgCl, which can be converted into tBu2CH-CH=O (three steps from tBu2C=O) or into tBu2C=CH-OSiMe3. Hydride transfer from NaBH 4 to tBu2CCl-CH=O affords tBu2CCl-CH 2OH, the transformations of which provide an entertaining set of SN1-type reactions. Several other examples of carbenium-type behavior are encountered in this gem-tBu2 system; they are attributed to steric congestion, which also impedes bond rotations in the anhydride and in two esters. A convenient route to tBu2CH-C≡N (five steps from tBu2C=O) uses the conversion of tBu2C=CH-OSiMe3 into tBu2CH-CH=NOH. The slow thermal (Z)/(E) equilibration of tBu2CH-NH-CH=O reveals the ranking of ecliptic repulsions as H 3C 2CH. Copyright
HETEROCUMULENES IN ACYLATION REACTIONS II. REACTIVITY OF ALKYL-SUBSTITUTED KETENES IN SPONTANEOUS HYDROLYSIS REACTIONS
Lyashchuk, S. N.,Skrypnik, Yu. G.
, p. 10 - 17 (2007/10/02)
The structures and electronic states of six ketenes were investigated by the semiempirical MNDO, MINDO/3, and AM1 quantum-chemical methods.The kinetics of the spontaneous hydrolysis of mono- and dialkylsubstituted ketenes in water and water-acetonitrile mixtures at 20 deg C were studied.The induction and steric effects of the substituents on the process rate were evaluated quantitatively in terms of a ρ? analysis.An increase in the number, length, and branching of the hydrocarbon substituents at the terminal carbon atom of the ketenes leads to a large decrease in the hydrolysis rate.The results of the calculations were compared with experimental data.Possible alternatives for the mechanism of the process are discussed.
Thioketene Syntheses, VI. Stable Thioketenes via Thionation of Sterically Hindered Acyl Chlorides
Schaumann, Ernst
, p. 2755 - 2765 (2007/10/02)
Sterically hindered acyl chlorides 11 are accessible via alkylation of the ester 1 or via chain elongation of the ketones 4 by one carbon atom in practicable, though multi-step reaction sequences.Action of phosphorus pentasulfide/pyridine on 11 leads to t
SYNTHESE EN SERIE ENCOMBREE. PREPARATION DE L'ACIDE DITERTIOBUTYL-METHYLACETIQUE tBu2MeCCOOH ET DE QUELQUES COMPOSES CETONIQUES DERIVES DE CETTE STRUCTURE
Dubois, Jacques-Emile,Zhang, Ben Li,Lion, Claude
, p. 4189 - 4194 (2007/10/02)
The synthesis of tBu2MeCCOOH, which is among the most sterically hindered known acids is described.Only Newman's sequence via tBu2C=O, tBu2MeCOH, tBu2C=CH2, tBu2CHCH2OH, tBu2CHCOOH, tBu2CHCOCl and tBu2C=C=O, which has been optimized in this work by a direct access to tBu2CHCOOH, permits the preparation of tBu2MeCCOOH.The condensation of the corresponding chloride with a Grignard reagent yields new highly-hindered ketones tBu2MeCCOR wich by alkylation give more substituted structures.The limitations of each method have been studied in this work.
