Acetone, enolization

Electrostatic potential map for acetone enolate shows most negatively-charged regions (in red) and less negatively-charged regions (in blue). 

HOMO of acetone enolate reveals most likely site of electrophilic attack. 

Other possible ambident nucleophiles include cyanii anion (CN ), methyl sulfinate anion (CH3SO2 ), ar acetone enolate (CH3COCH2 ). Identify the most electro rich atom(s) in each anion (based on charges alone), ar indicate the major product that should result from an S, reaction with methyl bromide at this atom(s). 

Examine the geometry and electrostatic potential map for acetone enolate. Are the CC and CO bonds in the enolate more similar to those in acetone or propen-2-ol precursors Is the negative charge primarily located on oxygen or on carbon Assuming this enolate is a hybrid of the two resonance contributors as shown above, which, if either, appears to be the major contributor ... 

Answer- Those are ideal TMs for alkylation of ethyl acetoaeetate (15) sinee 1,2 C-C disconneetion gives acetone enolate (14) for which (15) is the synthetic equivalent (p T i08 ). 

It is also possible to use the dilithium derivative of acetoacetic acid as the synthetic equivalent of acetone enolate.49 In this case, the hydrolysis step is unnecessary and decarboxylation can be done directly on the alkylation product. 

The anion of nitromethane is particularly reactive in S l reactions. Various kinds of tertiary nitro groups are replaced by a nitromethyl group on treatment with the anion of nitromethane (Section 7.1).49 2-Iodoadamantane reacts with the anion of nitromethane in the presence of acetone enolate (entrainment reaction) under irradiation of a 400-W UV lamp to give 2-ni-tromethyladamantane in 68% yield, (see Eq. 5.32).50a 1-Iodoadamantane also reacts with the anion of nitromethane in a similar way.50b... 

Examples of this approach to the synthesis of ketones and carboxylic acids are presented in Scheme 1.6. In these procedures, an ester group is removed by hydrolysis and decarboxylation after the alkylation step. The malonate and acetoacetate carbanions are the synthetic equivalents of the simpler carbanions lacking the ester substituents. In the preparation of 2-heptanone (entries 1, Schemes 1.5 and 1.6), for example, ethyl acetoacetate functions as the synthetic equivalent of acetone. It is also possible to use the dilithium derivative of acetoacetic acid as the synthetic equivalent of acetone enolate.29 In this case, the hydrolysis step is unnecessary, and decarboxylation can be done directly on the alkylation product. 

These heterocyclic compounds undergo many reactions which are similar to those of the acetone enolate. Thus, Claisen condensation and o-sulfonylation are exemplified by Scheme 57. 

Halothiophenes undergo photostimulated reaction with acetone enolate ion to form substitution products (76H(5j377). This is believed to occur by the radical-chain SrnI mechanism. The propagation steps are as follows ... 

Here ArX is the halothiophene and ArY the product. The nature of the initiation and termination steps is not known. Thus irradiation of 3-bromothiophene in liquid ammonia in presence of potassium acetone enolate gives the monothienylation product (492 51%) and the dithienylation product (493 25%). Instead of employing photostimulation, the reaction can be brought about in lower yields by dissolving sodium or potassium metal in the liquid ammonia solution. Here the corresponding alcohol is a side product. 

The vertical electron affinity (EA) of acetone is given as —1.51 eV by Jordan and Burrow386. Lifshitz, Wu and Tiernan387 determine—among other compounds—the excitation function and rate constants of the slow proton transfer reactions between acclone-Ih, acetone-Dg and other ketones. The acetone enolate anion has been produced in a CO2 laser induced alkane elimination from alkoxide anions by Brauman and collaborators388-390. These show, e.g. that the methane elimination from t-butoxide anion is a stepwise process ... 

By way of studying alternate methods to generate aryl radicals, Bunnett et al. found that halobenzenes react with acetone enolate ions... 

The photoinitiated reaction of diethylphosphite ion with iodobenzene has been examined in different solvents [60]. The reaction of acetone enolate ion with 2-chloroquinoline, under the same irradiation times, suffers a strong dependence on solvent nature. Thus, the yield of substitution product decreases going from liquid ammonia (90%) to THF (82%), DMF (74%), dimethoxyethane (28%), diethyl ether (9%), or benzene (4%) [61]. For this reason, the reactions are usually performed in liquid ammonia or DMSO under irradiation. 

It is known that acetone enolate anion does not react with primary alkyl radicals, and that nitromethane anion is not capable of initiating the SRN1 reactions even under irradiation [99]. Thus, the photo stimulated reactions of 25 with nitromethane anion as nucleophile and acetone enolate anion as entrainment reagent (which enables SRN1 initiation but cannot compete with the coupling of the methylene radical with nitromethane anion after cyclization) render the cyclized products 26 (Sch. 25) [98]. 

To liquid ammonia (25 mL) under argon contained in a three-necked flask fitted with a dry-ice condenser, acetone is added (4 mmol) along with one equivalent amount of t-BuOK. To the solution of the acetone enolate thus formed, 2-bromo-3,4,5-trimethoxybenzamide is added and the reaction mixture is irradiated in a photochemical reactor. The reaction is quenched by addition of NH4C1 (0.5 g) when all the substrate has been allowed to react. The ammonia is evaporated and slightly acidified water (50 mL... 

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