Dimethyl ketal

LiBF4, wet CH3CN, 96% yield.Unsubstituted 1,3-dioxolanes are hydrolyzed only slowly, but substituted dioxolanes are completely stable.This reagent proved excellent for hydrolysis of the dimethyl ketal in the presence of the acid-sensitive oxazolidine. ... 

DMSO, H2O, dioxane, reflux, 12 h, 65-99% yield.These conditions cleave a dimethyl ketal in the presence of a r-butyldimethylsilyl ether. 

LiBp4, wet CHjCN. Unsubstituted 1,3-dioxolanes are cleaved slowly under these conditions (40% in 5 h). The 4,5-dimethyl- and 4,4,5,5-tetra-methyldioxolane and 1,3-dioxane are inert under these conditions. Dimethyl ketals are readily cleaved. 

The direct formation of a dimethyl ketal by reaction of the ketone with methanol is particularly sensitive to steric effects. Only cyclohexanones react under these conditions.In the steroid series only saturated 3-ketones form dimethyl ketals with methanol and acid although partial reaction of a 2-ketone has been observed in the presence of homogenous rhodium catalyst. ... 

Dimethyl ketals and enol ethers are stable to the conditions of oxime formation (hydroxylamine acetate or hydroxylamine hydrochloride-pyridine). Thioketals and hemithioketals are cleaved to the parent ketones by cadmium carbonate and mercuric chloride. Desulfurization of thioketals with Raney nickel leads to the corresponding methylene compounds, while thioenol ethers give the corresponding olefin. In contrast, desulfurization of hemithioketals regenerates the parent ketone. ... 

The dimethyl ketal function (51) is one of the most suitable base stable protecting groups for saturated 5a- and 5/i-3-ketones. It is formed by reaction of the ketone (50) with methanol in the presence of a suitable catalyst. Good selectivity can also be achieved with this group since 2-, 6-, 11-, 12-, 17- and 20-ketones do not form dimethyl ketals under these conditions. The 2-ketone is converted in part to the dimethyl ketal in the presence of homogeneous rhodium catalyst. "" y -Toluenesulfonic acid is the catalyst of... 

Estr-5(10)-en-3-ones also react with methanol to give dimethyl ketals. Weak acid catalysts such as malonic and oxalic acid or selenium dioxide, which are unable to promote conjugation of the double bond, are conveniently used. ... 

Enol ethers of saturated 3-ketones are not usually obtained directly from the ketone and therefore are of little importance as protective groups. However, enol ether (52) has been used instead of the bulkier 3-dimethyl ketal to protect the 3-ketone during angular methylation to (53). ... 

Strong 1 3 interactions between the axial substituent at C-6 with 8j5- and 2ji (5a-series) hydrogens and 10 -substituents decrease the reactivity of the 6-ketone as compared to saturated 3-ketones. The 6-ketone does not react with methanol to give a dimethyl ketal, even in the absence of the C-19 methyl group. Thus the 19-nor-5a-3,6-dione (75) gives selectively the 3,3-dimethyl-ketal (76). ... 

Camphor dimethyl ketal, TMSOTf, DMSO, 90°, 3 h, 25% yield. ... 

The direct conversion of dimethyl ketals to other carbonyl protected derivatives is also possible. Treatment of a dimethyl ketal with HSCH2CH2SH, TeCl4, CICH2CH2CI gives the dithiolane in 99% yield." ... 

H2Sil2, CDCI3, —42°, 1-10 min, 100% yield. Aromatic ketals are cleaved faster than the corresponding aliphatic derivatives, and cyclic ketals are cleaved more slowly than the acyclic analogues, such as dimethyl ketals. Substituted ketals such as those derived from butane-2,3-diol, which react only slowly with Mc3SiI, can also be cleaved with H2Sil2. If the reaction is run at 22°, ketals and acetals are reduced to iodides in excellent yield. 

HSCH2CH2SH, SnCl2-H20, THF, reflux, 10-240 min, 51-96% yield." Under these conditions, aldehydes react faster than ketones. Dimethyl ketals, which react faster than dimethyl acetals, are also converted to... 

Acid treatment hydrolyzes dimethyl ketal by-products, which form to the extent of 5-10% during the reaction. 

Spectra obtained by 1H NMR allowed the progress of the hydrogenolysis reaction to be followed quantitatively. The cyclopropyl protons in the polymer have an 1H NMR peak at 61.0 ppm, while the protons on the ring-opened, gem-dimethyl repeat unit (Equation A) have an XH NMR peak at 61.35 ppm. The gem-dimethyl peak assignment was based on chemical shift calculations (17). Also the dimethyl acetal of acetone has protons in a similar chemical environment to those on the gem-dimethyl ketal repeat unit and they have a chemical shift between 61.3 ppm and 61.A ppm (18). A proton NMR spectrum of partially hydrogenated polycyclopropanone is shown in Figure 7. 

A further convenient preparation of 7 was found30 to be the hydrolysis of cyclopropenone dimethyl ketal (22)31 ... 

A value of kjkp = 17 000 has been determined for partitioning of the acetophenone oxocarbenium ion [12+] in water.15,16 It is not possible to estimate an equilibrium constant for the addition of water to [12+], because of the instability of the hemiketal product of this reaction. However, kinetic and thermodynamic parameters have been determined for the reaction of [12+] with methanol to form protonated acetophenone dimethyl ketal [12]-OMeH+ and for loss of a proton to form a-methoxystyrene [13] in water (Scheme 10).15,16 Substitution of these rate and equilibrium constants into equation (3) gives values of AMeoH = 6.5 kcal mol-1 and Ap = 13.8 kcal mol-1 for the intrinsic... 

For instance, 2-methylpropene reacted with acetic acid at 18°C in the presence of Al-bentonite to form the ester product (75). Ion-exchanged bentonites are also efficient catalysts for formation of ketals from aldehydes or ketones. Cyclohexanone reacted with methanol in the presence of Al-bentonite at room temperature to give 33% yield of dimethyl ketal after 30 min of reaction time. On addition of the same clay to the mixture of cyclohexanone and trimethyl orthoformate at room-temperature, the exothermic reaction caused the liquid to boil and resulted in an almost quantitative yield of the dimethyl ketal in 5 min. When Na- instead of Al-bentonite is used, the same reaction did not take place (75). Solomon and Hawthorne (37) suggest that elimination reactions may have been involved in the geochemical transformation of lipid and other organic sediments into petroleum deposits. 

Kekule structure org chem A molecular structure of a cyclic conjugated system that is depicted with alternating single and double bonds. ka-k3,la. strak-char j ketal oRG CHEM 1. Former term for the =CO group, as in dimethyl ketal (acetone). 2. Any of the ketone acetates from condensation of alkyl orthoformates with ketones in the presence of alcohols. ke,tal ... 

Synonyms ACN AI3-01238 BRN 0635680 Caswell No. 004 CCRIS 5953 Chevron acetone Dimethylformaldehyde Dimethyl ketal Dimethyl ketone DMK EINECS 200-662-2 EPA pesticide chemical code 004101 FEMA No. 3326 Ketone propane p Ketopropane Methyl ketone NSC 135802 Propanone Propan-2-one 2-Propanone Pyroacetic acid Pyroacetic ether RCRA waste number U002 Sasetone UN 1090. UN 1091. 

Dimethylhexane, see 3-Methylheptane asjm-Dimethylhydrazine, see 1,1-Dimethylhydrazine A.A-Dimethylhydrazine, see 1,1-Dimethylhydrazine Uflsjm-Dimethylhydrazine, see 1,1-Dimethylhydrazine Dimethyl ketal, see Acetone... 

Other related reactions involve TV-fluorenylmethyloxycarbonyl (N-Fmoc) AAs and aliphatic aldehydes (83JOC77) or substituted /-butoxycarbonyl (N-Boc) Aas and 2,2-dimethyoxypropane (acetone dimethyl ketal) (84TL5855 87JOC2361 88TL2019), as well as A-(dimethylthio)methylene derivatives of an AA and aromatic aldehydes [89JCS(P1)1577]. 

Reductive Carbonylation of Dimethoxy Ketals and Dimethyl Carbonate. Acetaldehyde is obtained via the reductive carbonylation of dimethyl ketals. Equation 12, and dimethyl carbonate. Equation 13 (15). 

Relative to the reductive carbonylation of methanol, the added recycle step is a disadvantage with dimethyl ketals. This disadvantage is offset by the lower pressure of operation and the noncorrosive halide-free catalyst, which permits cheaper materials of construction. 

Reaction of 2,2-dichloro-3,3-dimethylcyclopropanone dimethyl ketal with trimethyl orthoisobutyrate to give trimethyl a-chloro-/ -methylortho-crotonate [176]. 

The method has been applied by the submitters2 to the preparation of cyclohexylmethylpropiolaldehyde diethyl acetal (54% yield) from cyclohexylmethylacetylene and triethyl orthoformate of phenylethynyl n-butyl dimethyl ketal (40% yield) from phenylacetylene and trimethyl -orthovalerate and of phenylethynyl methyl diethyl ketal (34% yield) from phenylacetylene and triethyl orthoacetate. w-B utylpropiolaldehyde diethyl acetal was isolated in 32% yield by heating an equimolar mixture of 1-hexyne and triethyl orthoformate containing catalytic amounts of a zinc chloride-zinc iodide catalyst under autogenous pressure at 190° for 3 hours. 

Homoallyl ethers. Trimethylsilyl triflate catalyzes a reaction between dimethyl ketals and allyltrimethylsilane to form homoallyl ethers. Allylation is not possible with the parent ketones. 

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