Acetone rearrangement

Pyrrolidin-l-yl)-7-trityl-2-azabicyclo[4.1.0]hepta-2,4-dieniumtetrafluoroborates, e.g. 34, on basification with potassium carbonate in acetone, rearrange spontaneously to 7-(pyrrolidin-l-yl)-3-trityl-3//-a/epines, e. g. 35.64... 

Griffiths and Gutsche (23) recently studied the interconversion of deuterated mandelaldehyde dimer and 2-hydroxyacetophenone in pyridine to obtain information concerning the glyceraldehyde-dihydroxy-acetone rearrangement. Their results support an enolization mechanism requiring a base and an acid catalyst. They found a deuterium isotope effect of ca. 1.3 for the transformation of the aldehyde to the ketone. When they corrected this for the apparently differing amounts of the aldehyde form in equilibrium with the proteo dimer and the deuterio dimer, they obtained a value of 3.9. By the Swain-Schaad equation (26) ... 

For example, barrelene (71), when photosensitized by acetone, rearranges to... 

Cyclooctatetraene can be obtained on an industrial scale by metal carbonyl catalyzed thermal tetramerization of acetylene. If cyclooctatetraene is UV-irradiated at low temperature in the presence of acetone, it is reversibly rearranged to form semibullvalene (H.E. Zimmerman, 1968, 1970). 

Isopropenyl acetate [108-22-5] which forms upon reaction of acetone [67-64-1] with anhydride, rearranges to acetylacetone [123-54-6] in the presence of BF3 (19) ... 

Linalool can be converted to geranyl acetone (63) by the CarroU reaction (34). By transesterification with ethyl acetoacetate, the intermediate ester thermally rearranges with loss of carbon dioxide. Linalool can also be converted to geranyl acetone by reaction with methyl isopropenyl ether. The linalyl isopropenyl ether rearranges to give the geranyl acetone. 

DAG is treated with ethanol and hydrochloric acid in the presence of inert solvent, eg, chlorinated solvents, hydrocarbons, ketones, etc. The L-ascorbic acid precipitates from the mixture as it forms, minimising its decomposition (69). Cmde L-ascorbic acid is isolated through filtration and purified by recrystallization from water. The pure L-ascorbic acid is isolated, washed with ethanol, and dried. The mother Hquor from the recrystallization step is treated in the usual manner to recover the L-ascorbic acid and ethanol contained in it. The cmde L-ascorbic acid mother Hquor contains solvents and acetone Hberated in the DAG hydrolysis. The solvents are recovered by fractional distillation and recycled. Many solvent systems have been reported for the acid-catalyzed conversion of DAG to L-ascorbic acid (46). Rearrangement solvent systems are used which contain only the necessary amount of water required to give >80% yields of high purity cmde L-ascorbic acid (70). 

The synthesis of dehydro-hnalool (28) rehes on the basic chemicals acetone and acetjiene. Addition of a metal acetyUde to acetone yields methylbutynol (33). Semihydrogenation affords the alkene (34) which is reacted with /-propenylmethyl ether. A Cope rearrangement of the adduct yields methyUieptenone (35). Addition of a second mole of metal acetyUde to dehydro-linalool (28) is followed by a second Cope rearrangement to yield... 

The precedent is strong for the involvement of oxetanes as Intermediates in carbonyl additions to pyrroles. " NMR evidence has been obtained far an oxetane adduct of acetone and N-methylpyrrole. The initial photoadduct was shown to rearrange readily on workup to the 3-(hydroxyalkyl)pyrrole derivative. 

The preparation of neopentyl alcohol from diisobutylene herein described represents an example of acid-catalyzed addition of hydrogen peroxide to a branched olefin, followed by an acid-catalyzed rearrangement of the tertiary hydroperoxide formed. In addition to neopentyl alcohol, there are formed acetone and also small amounts of methanol and methyl neopentyl ketone by an alternative rearrangement of the hydroperoxide. 

Another feature of systems that are subject to B-strain is their reluctance to form strained substitution products. The cationic intermediates usually escape to elimination products in preference to capture by a nucleophile. Rearrangements are also common. 2-Methyl-2-adamantyl p-nitrobenzoate gives 82% methyleneadamantane by elimination and 18% 2-methyl-2-adamantanol by substitution in aqueous acetone. Elimination accounts for 95% of the product from 2-neopentyl-2-adaman l p-nitrobenzoate. The major product (83%) from 2-r-butyl-2-adamantyl p-nitrobenzoate is the rearranged alkene 5. 

The photolysis of benzobarrelene. A, has been studied in considerable detail. Direct photolysis gives C, but when acetone is used as a photosensitizer, the di-rc-methane rearrangement product B is formed. 

Kubota and co-workers describe a novel oxidative rearrangement of the diosphenol (58) of 17iS-hydroxyandrost-4-ene-2,3-dione to the A-nor-A -1,2-diketone (59) in 33 % yield by the action of specially prep d manganese dioxide in boiling acetone. The rate of ring contraction is very sensitive to the source of the oxidant, and a trace of dilute sulfuric acid in the reaction mixture causes oxidative fission of ring A. 

The coupling of enamines with aromatic diazonium salts has been used for the syntheses of monoarylhydrazones of a-diketones (370,488-492) and a-ketoaldehydes (488,493). Cleavage of the initial enamine double bond and formation of the phenylhydrazone of acetone and acetophenone has been reported with the enamines of isobutyraldehyde and 2-phenylpropionalde-hyde. Rearrangement of the initial coupling product to the hydrazone tautomer is not possible in these examples. 

The di- r-methane rearrangement is a fairly recent reaction. One of the first examples has been reported in 1966 by Zimmerman and Grunewald with the isomerization of barrelene 8 to semibullvalene 9. This rearrangement reaction occurs in the presence of acetone as photosensitizer, and proceeds from the Ti-state. ... 

Yields of the di- r-methane rearrangement reaction strongly depend on substrate structure, and are ranging from poor to nearly quantitative. Acetone and acetophenone have been used as photosensitizers." ... 

The required vicinal diols are in general accessible by standard methods. Pinacol itself can be obtained by dimerization of acetone. For the rearrangement reaction concentrated or dilute sulfuric acid is often used as catalyst. 

Oxepin has also been converted photochemically to phenol in 74% yield. This reaction occurs under irradiation conditions by which benzene oxide is excited to a triplet state, e.g. by irradiation in acetone as solvent.207 A rare example for a nucleophilic catalysis of the aromatization of an oxepin/benzene oxide to a phenol has been reported for /err-butyl oxepin-4-carboxylate which undergoes a rearrangement reaction in the presence of trimethylamine to give a mixture of /m-butyl 3-hydroxybenzoate (94%) and 4-hydroxybenzoate (6%).243... 

Nitroso-5//-dibenz[/j,/ azepine (see Section 3.2.1.5.4.1.) in methanolic hydrochloric acid undergoes rearrangement and ring contraction to a mixture of acridine (59%), acridine-9-carbaldehyde (trace), and 2-nitro-5//-dibenz[/ ,/ azepine (3% mp 176-178 C).184 However, in acetone and hydrochloric acid, the aldehyde (57 %) becomes the major product. On thermolysis, (or photolysis in the presence of oxygen), in hydroxylic solvents, the nitroso compound yields mainly acridine (36-76%) together with minor amounts of either 2-nitrodibenzazepine (4-6% by thermolysis) or acridine-9-carbaldehyde (18% by photolysis). However, in non-hydroxylic solvents, e.g. cumene, acridine-9-carbaldehyde (64%) is the major product. 

Many radicals undergo fragmentation or rearrangement in competition with reaction with monomer. For example, f-butoxy radicals undergo p-scission to form methyl radicals and acetone (Scheme 3.6). 

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