Enolate Salts Research Articles

C–C bond-forming reactions of ground-state aryl halides under reductive activation

Under basic conditions aryl halides can undergo SRN1 reactions, BHAS reactions and benzyne formations. Appropriate complex substrates afford an opportunity to study inherent selectivities. SRN1 reactions are usually favoured under photoactivated conditions, but this paper reports their success using ground-state and transition metal-free conditions. In benzene, the enolate salt 12, derived by deprotonation of diketopiperazine 11, behaves as an electron donor, and assists the initiation of the reactions, but in DMSO, it is not required. The outcomes are compared and contrasted with a recent photochemical study on similar substrates. A particular difference is the prevalence of hydride shuttle reactions under relatively mild thermal conditions.

Mechanistic investigation and DFT calculation of the new reaction between S-methylisothiosemicarbazide and methyl acetoacetate

A study on the synthesis and mechanistical aspects of formation of 3-methyl-5-oxo-3-pyrazolin-1-carboxamide (MOPC) starting from S-methylisothiosemicarbazide hydrogen iodide and methyl acetoacetate was performed. In the alkaline aqueous solution, the intermediate methyl acetoacetate S-methylisothiosemicarbazone undergoes substitution of CH3S− anion by hydroxide anion, cyclization, carbanion formation, and elimination of methanol, thus yielding corresponding Na-enolate salt of pyrazol-5-one derivative. The structure of the compound obtained after protonation of the formed enolate salt was determined by means of spectroscopic techniques and single-crystal X-ray diffraction analysis. The mechanism of conversion of methyl acetoacetate S-methylisothiosemicarbazone into MOPC was investigated by means of the B3LYP functional, and it was found that the reaction is thermodynamically controlled.

ChemInform Abstract: Synthesis of α‐Silylcarboxylic Acids.

AbstractThe lithium enolate salt derived from silyl acetate (I) readily undergoes C‐silylation to give the desired silylcarboxylic acids.

Mechanistic Studies of the O2-Dependent Aliphatic Carbon−Carbon Bond Cleavage Reaction of a Nickel Enolate Complex

The mononuclear nickel(II) enolate complex [(6-Ph(2)TPA)Ni(PhC(O)C(OH)C(O)Ph]ClO(4) (I) was the first reactive model complex for the enzyme/substrate (ES) adduct in nickel(II)-containing acireductone dioxygenases (ARDs) to be reported. In this contribution, the mechanism of its O(2)-dependent aliphatic carbon-carbon bond cleavage reactivity was further investigated. Stopped-flow kinetic studies revealed that the reaction of I with O(2) is second-order overall and is ∼80 times slower at 25 °C than the reaction involving the enolate salt [Me(4)N][PhC(O)C(OH)C(O)Ph]. Computational studies of the reaction of the anion [PhC(O)C(OH)C(O)Ph](-) with O(2) support a hydroperoxide mechanism wherein the first step is a redox process that results in the formation of 1,3-diphenylpropanetrione and HOO(-). Independent experiments indicate that the reaction between 1,3-diphenylpropanetrione and HOO(-) results in oxidative aliphatic carbon-carbon bond cleavage and the formation of benzoic acid, benzoate, and CO:CO(2) (∼12:1). Experiments in the presence of a nickel(II) complex gave a similar product distribution, albeit benzil [PhC(O)C(O)Ph] is also formed, and the CO:CO(2) ratio is ∼1.5:1. The results for the nickel(II)-containing reaction match those found for the reaction of I with O(2) and provide support for a trione/HOO(-) pathway for aliphatic carbon-carbon bond cleavage. Overall, I is a reasonable structural model for the ES adduct formed in the active site of Ni(II)ARD. However, the presence of phenyl appendages at both C(1) and C(3) in the [PhC(O)C(OH)C(O)Ph](-) anion results in a reaction pathway for O(2)-dependent aliphatic carbon-carbon bond cleavage (via a trione intermediate) that differs from that accessible to C(1)-H acireductone species. This study, as the first detailed investigation of the O(2) reactivity of a nickel(II) enolate complex of relevance to Ni(II)ARD, provides insight toward understanding the chemical factors involved in the O(2) reactivity of metal acireductone species.

Fluoride‐Triggered Domino Reactions Involving Ammonium Acetylides and Carbonyl Compounds

AbstractWe describe the use of tetrabutylammonium fluoride as a basic trigger for reactions capable of generating structurally diverse products from methyl propiolate and carbonyl derivatives. The processes are based on either chemodifferentiating multicomponent ABB′ three‐component reactions or bimolecular domino reactions, and they operate through three different and well‐defined autocatalytic cycles. These catalytic cycles share a common property: they are launched by the acid–base reaction of fluoride ions to give catalytic amounts of acetylide or enolate salts, but they are maintained by the autocatalytic generation of these salts.

An efficient synthesis of N1-substituted 2,5-dioxo-1,2,5,6,7,8-hexahydro-3-quinolinecarboxamide via enolate salts

Various 2-(2-cyano-2-carbamoyl-1-ethenyl)-5,5-dimethyl-3-oxo-1-cyclohexen-1-olates substituted in the amide group with dialkylammonium or sodium cations were prepared via reactions of N-substituted cyanoacetamides with dimedone–DMFDMA adduct by a one-pot, two-step protocol. The salts obtained were used in reactions with N-nucleophiles for further synthesis of the N1-substituted 2,5-dioxo-1,2,5,6,7,8-hexahydro-3-quinolinecarboxamides that are analogues of well-known pharmaceuticals. The structure of the salts and the N1-substituted 2,5-dioxo-1,2,5,6,7,8-hexahydro-3-quinolinecarboxamides was established by means of spectroscopic and X-ray diffraction studies.

New Practical Synthesis of Tenidap

The development of a new, practical synthesis to tenidap is described. N,O-Dialkoxy(aryloxy)carbonylation of 5-chloro-2-oxo-2,3-dihydroindole, followed by removal of the O-alkoxy(aryloxy)carbonyl group gave 1-[alkoxy(aryloxy)carbonyl]-5-chloro-2-oxo-2,3-dihydroindoles in good yields. The latter compounds were thenoylated in the 3-position. The role of DMAP in the acylation reaction is discussed. The structures of the thenoylated products and their enolate salts were investigated both in solution and solid phases. Ammonolysis of 5-chloro-3-[1-hydroxy-1-(2-thienyl)methylene]-2-oxo-1-phenoxycarbonyl-2,3-dihydroindole afforded the corresponding 1-carbamoyl derivative (tenidap) in high yield. The corresponding 1-ethoxy- and 1-methoxycarbonyl derivatives could not be similarly transformed to tenidap; loss of the alkoxycarbonyl moiety occurred instead of carbamoylation.

Thermal Catalytic Depolymerization of Poly(L-Lactic Acid) Oligomer into LL-Lactide: Effects of Al, Ti, Zn and Zr Compounds as Catalysts.

A series of Al, Ti, Zn and Zr compounds, ie., their metal alkoxides, organic acid and enolate salts, halid and oxide, were evaluated as intramolecular transesterification catalysts for the thermal depolymerization reaction of poly(L-lactic acid) oligomer resulting in LL-lactide, meso-lactide and DD-lactide by gas chromatography using a β-cyclodexstrin chiral stationary phase capillary column. The activity of the intramolecular transesterification compared with that of stannous 2-ethylhexanoate was in the following order: Sn>Zn>Zr>Ti>Al.

α-Arylation of ketones by aryllead triacetates. Effect of methyl and phenyl substitution at the α position

An examination of the α-arylation of a number of ketones and their enolate salts by p-methoxyphenyllead triacetate provides further evidence for a very marked selectivity in the arylation reaction. It is found that the reaction proceeds well at tertiary α-carbons and at secondary centres activated by the presence of a phenyl group, but fails where the secondary centre is unactivated and at primary α-carbons.

Formation and Reactivity of Highly Stabilized Carbanions and Enolates by Pd-Catalyzed Alkylation of Heterocyclic Compounds

Highly stabilized carbanion and enolate salts, heterocycle-substituted sodiomalononitrile and sodiocyanoacetates, were synthesized via Pd-catalyszed ring-alkylation of bromoheterocyclic compounds and shown to be useful intermediates for the synthesis of various alkyl-substituted heterocyclic compounds

Synthesis and carbon-carbon bond-forming reactions of tungsten, molybdenum, and rhenium enolates

Abstract

Zur Reaktionsweise von Diphenylcyclopropenon mit β‐Carbonyl‐enolaten. I. Einsatz von Acetylaceton, Acetessigsäure‐methylester, 2‐Äthoxycarbonyl‐cyclododecanon und Malonsäure‐dimethylester

Reaction of Diphenylcyclopropenone with β‐Carbonyl‐enolates. I. Use of Acetylacetone, Methyl Acetoacetate, 2‐Ethoxycarbonyl‐cyclododecanone and Dimethyl MalonateThe reaction of the sodium salts of acetylacetone (6), methyl acetoacetate (7), 2‐ethoxycarbonyl‐cyclododecanone (8), dimethyl malonate (19) and its methyl derivative 20 with diphenylcyclopropenone (5) in dimethylformamide at room temperature led to the unsaturated γ‐lactones 14, 15, 17, 22 and 36. In the case of dimethyl malonate (19), the halfester 21, the acyl‐malonic ester 24 and the indenone‐malonic ester 23 were also isolated.Several intermediates and the final products were characterised by reactions and spectroscopically. A general mechanism is discussed for the addition of cyclo‐propenones (1) to the enolate salts of β‐dicarbonyl compounds 4 involving the bicyclic lactone‐enolates 18 and 32 as intermediates. The products formed via 18 and 32 are considered to be the result of an attack of one of the oxygen atoms of the β‐carbonyl‐enolate anion (4), the product 24, on the other hand, of the attack of the α‐carbon atom of 4; in both cases the attack is on the carbonyl C‐atom of 5.

ChemInform Abstract: REACTIVITY AND ION PAIRING OF ALKALI β‐KETOENOLATES

AbstractLösungen von Alkalimetallund Tetrabutylammoniumsalzen von Dibenzoylmethan und Dipivaloylmethan in Dimethylsulfoxid und THF werden durch eine Reihe vonvMethoden zur Bestimmung des Grades der Assoziation und der Natur der assoziierten Spezies untersucht.

ChemInform Abstract: METHOD FOR THE SYNTHESIS OF 4‐SUBSTITUTED ACETOACETATES

AbstractAcetessigsäureethylester wird durch Bromierung und Umsetzung mit den Nucleophilen (IV) zu den Derivaten (VI) substituiert.

Method for the synthesis of 4-substituted acetoacetates

Ethyl 4-bromo-3-oxobutyrate can be converted with sodium hydride into the enolate salt and nucleophilic substitutions can thereafter be carried out at the 4-carbon atom.

ChemInform Abstract: ALKYLATION OF 1‐METHYL‐2‐PIPERIDONES

In the course of our investigation which led to the development of a new stereoelectronic theory for the hydrolysis of amidesl it was necessary to prepare N-dialkylated imidate salts. Some of those salts can be easily produced from the appropriate 3-alkyl-I-methyl-2-piperidones. The direct alkylation of 1 -methyl-2-piperidones was therefore considered. The a-alkylation of I-methyl-2-pyrrolidone (3) and of N,N-dialkylamides (4) has been reported but the yields were moderate.' This is presumably due to the base used (NaNH,) to produce the enolate salt of the amide function because when n-butyl lithium was used to generate the dilithioamide of secondary amide, high yield of a-alkylated secondary amides was obtained (6). We would like to report the optimum experimental conditions that we have found for the alkylation reaction of N-methyl six-membered lac tam^.^ We have found that I-methyl-2-piperidone (1) can be converted into 2 or 3 in high yield with the proper alkyl iodide. The lithium enolate of 1 was generated with lithium dimethylamide in benzene. A slight excess of the base and alkylating agent ensured complete alkylation. There were no detectable amounts of 0-alkylated or bis-alkylated products. 1,3-Dimethyl-2-piperi-

The formation of ethynylferrocenes in reactions of sterically crowded acetylferrocenes with a grignard reagent

Acetylferrocenes bearing a bulky 2-alkyl substituent react with isopropylmagnesium bromide to give enolate salts which are converted into ethynylferrocenes by a thermally induced elimination reaction.

Negatively charged electrophiles. Acylation of strong nucleophiles by enolate salts of .beta.-keto esters

Negatively charged electrophiles. Acylation of strong nucleophiles by enolate salts of .beta.-keto esters

A total synthesis of (±)-ethyl acorate {(±)-ethyl (3RS)-3-[(1SR,4SR)-1-isobutyryl-4-methyl-3-oxocyclohexyl]butyrate} and (±)-epiacoric acid. An application of the generation and alkylation of a specific enolate

After the failure of appropriate conjugate additions to the model ketone methyl 3-(3-oxocyclohex-1-enyl)butyrate (5a), a mixture of (±)-ethyl acorate (1; R = Et)(see title) and (±)-ethyl epiacorate (20)(the 3-epimer) was obtained by manipulation of the addition product (13b) of a cis–trans mixture of but-2-enonitrile and the enolate anion generated by lithium–ammonia reduction of 1-isobutyryl-4-methylcyclohex-3-enyl acetate (12). Similar reductions of α-acetoxy-ketones may represent another general method for the production of specific enolate salts.

Polymeric ligands. IV. Vinyltriacylmethanes

AbstractMethacrylylacetylacetone and acrylylacetylacetone were prepared by acylation of acetylacetone enolate salts with methacrylyl chloride and acrylyl chloride, respectively. Both monomers yielded poor homopolymers. Methacrylylacetylacetone formed copolymers with styrene and methyl methacrylate without difficulty.