The aldo-cis-trans-enolic equilibrium of substituted alkyl formylacetates and alkyl formylmethylphosphonates

Yoffe, S.T.; Petrovsky, P. V.; Goryunov, Ye. I.; Yershova, T.V.; Кабачник, М. И.

doi:10.1016/0040-4020(72)80114-5

Cited by 24 publications

(13 citation statements)

References 10 publications

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“…While analyzing alternative approaches for pyridine construction, we have paid attention on diethyl ethoxymethylencyanophosphonate 3d, which potentially should be a useful reagent in different cyclizations. To our surprise there are only two papers of the same authors describing the synthesis of 3d in very low yield and subsequent reaction with alkali [18,19]. Our attempts to improve the described procedure and to prepare the phosphonate 3d by interaction of triethyl ortoformate with diethyl cyanomethylphosphonate in acetic anhydride gave approximately the same low yields as in original work.…”

Section: Synthesis Of Trifluoromethylated Pyridines Condensed With Sumentioning

confidence: 47%

“…Without purification 3c was subsequently treated with acetic anhydride to furnish phosphonate 3d as a single stereoisomer in reasonable yield (Scheme 3). It should be noted that in the 1 H NMR spectra of vinylphosphonates cis-vicinal coupling constants 3 J HP are in the range of 7-15 Hz, whereas trans-vicinal constants are much bigger and usually comprise 30-40 Hz [19]. Since the corresponding value observed by us for 3d is equal to 8.8 Hz, it indicates that hydrogen and the phosphonate substituent at the C5 5C-bond of 3d are cis-oriented to each other.…”

Section: Synthesis Of Trifluoromethylated Pyridines Condensed With Sumentioning

confidence: 90%

“…The reaction mixture was diluted with CHCl 3 (50 mL), washed with 20% aqueous solution of NaCl (20 mL), dried over Na 2 SO 4 and after evaporation of solvent the residue was distilled in vacuum to afford the phosphonate 3d (14.45 g, 62%) as a colorless liquid, bp 160-162 8C (0.4 Torr) (lit. [19] 160-162 8C…”

Section: Preparation Of Diethyl Ethoxymethylencyanophosphonate (3d)mentioning

confidence: 98%

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1-Bromo-2-trifluoroacetylcyclobutenes as novel building blocks for the construction of trifluoromethyl substituted heterocycles. Part 3: Synthesis of trifluoromethylsubstituted pyridines, condensed with cyclobutene moieties

Koldobskií

Solodova

Godovikov

et al. 2010

Journal of Fluorine Chemistry

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Section: Synthesis Of Trifluoromethylated Pyridines Condensed With Sumentioning

confidence: 47%

Section: Synthesis Of Trifluoromethylated Pyridines Condensed With Sumentioning

confidence: 90%

Section: Preparation Of Diethyl Ethoxymethylencyanophosphonate (3d)mentioning

confidence: 98%

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1-Bromo-2-trifluoroacetylcyclobutenes as novel building blocks for the construction of trifluoromethyl substituted heterocycles. Part 3: Synthesis of trifluoromethylsubstituted pyridines, condensed with cyclobutene moieties

Koldobskií

Solodova

Godovikov

et al. 2010

Journal of Fluorine Chemistry

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“…The coupling constant JP-H1.,I being 13-14 Hz as seen in 1H NMR strongly suggested this cis relationshipt (14,15). An x-ray analysis on lgt confirmed that it was not only 100% enolized but also existed as stereoisomer 2 solely (unpublished data).…”

Section: IImentioning

confidence: 75%

“…In a typical experiment, triethylphosphite (7.0 ml, 41 mmol) was added dropwise over 10 min to neat acid chloride (32 mmol) under nitrogen (in the case of li, triethylphosphite was added to a solution of p-nitrophenylacetyl chloride in dry tetrahydrofuran). After addition, the mixture was stirred at 60'C for 3 hr and then at 250C for 15 hr. Products were obtained in 60-90% yields.…”

Section: IImentioning

confidence: 99%

Enol-keto tautomerism of α-ketophosphonates

Tam

Mattocks

Tishler

1981

Proc. Natl. Acad. Sci. U.S.A.

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A number ofa-ketophosphonates have been prepared and their enol-keto tautomerism has been studied by means ofproton and phosphorus NMR and infrared spectroscopy and the ferric chloride test. Aliphatic ketophosphonates exist largely in the keto tautomeric forms, with only a small amount of enol forms present. All the aromatic acylphosphonates studied, however, enolize extensively. An x-ray analysis confirmed enolization and E configuration as the only stereochemical isomer. Reaction of diazomethane with diethyl p-methoxyphenylacetyl phosphonate gave a mixture of 0-methylation and carbene insertion products, whereas the same reaction with diethyl isobutyryl phosphonate gave only carbene insertion products.Recent publications have indicated that a number of amino phosphonic acids, as such or in small peptides, possess biological activities (1-4) and therefore can be considered as bioisosteres of the amino carboxylic acids. In a program designed to synthesize some specific peptides containing a phosphonic acid residue, we have had occasion to prepare some a-amino phosphonic acids by the reported procedures involving the conversion of the appropriate alkyl a-ketophosphonate into its oxime followed by reduction of the latter (5-7). In this work, we noticed that some ofthe ketophosphonates we prepared produced pronounced color changes with ferric chloride, suggesting that these compounds exist as enols. Inasmuch as we found no literature reports on the enol-keto tautomerism of a-ketophosphonates, it was of interest to investigate this phenomenon by comparing it to the situation with substituted pyruvic acids (8) and esters (9). RESULTS AND DISCUSSIONThe diethyl ketophosphonates la-li (Scheme 1) were prepared Qualitative and quantitative studies of the keto-enol tautomerism ofthese a-ketophosphonates were based on results offerric chloride color test, proton and phosphorus NMR, and infrared spectroscopy. We chose to investigate the tautomerism by using NMR rather than the classical Kurt Meyer bromine titrations (12) because of convenience. For this, we established the enol-keto tautomerism of methyl phenylpyruvate by NMR and found it to approximate the results obtained by Stock et al. (9) using bromine titrations.The proton NMR characteristics of the a-ketophosphonates shown in Scheme 1 were examined in chloroform-dl (Table 1).Each of the aliphatic diethyl ketophosphonates la-ic exhibited a signal around 3 ppm with appropriate splitting, indicating the presence of the methylene protons (in la and ic) or methine proton (in lb) attached to a carbon atom adjacent to a carbonyl function. No vinylic proton was observed in the downfield region. This strongly suggested that these aliphatic diethyl ketophosphonates exist predominantly in the keto tautomeric form, although the presence ofa small singlet at 1.14 ppm (about 5%) in addition to the large singlet at 1.04 ppm (95%) for the t-butyl group in Ic suggested the presence of about 5% enol form in this case (this was supported by evidence of 31P NMR, see below). One ...

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NMR, IR, conformation and hydrogen bonding

Floris

1990

PATAI'S Chemistry of Functional Groups

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The aldo-cis-trans-enolic equilibrium of substituted alkyl formylacetates and alkyl formylmethylphosphonates

Cited by 24 publications

References 10 publications

1-Bromo-2-trifluoroacetylcyclobutenes as novel building blocks for the construction of trifluoromethyl substituted heterocycles. Part 3: Synthesis of trifluoromethylsubstituted pyridines, condensed with cyclobutene moieties

1-Bromo-2-trifluoroacetylcyclobutenes as novel building blocks for the construction of trifluoromethyl substituted heterocycles. Part 3: Synthesis of trifluoromethylsubstituted pyridines, condensed with cyclobutene moieties

Enol-keto tautomerism of α-ketophosphonates

NMR, IR, conformation and hydrogen bonding

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