Synthesis and properties of a series of sterically hindered guanidine bases

Barton, Derek H. R.; Elliott, John D.; Géro, S. D.

doi:10.1039/p19820002085

Cited by 119 publications

(56 citation statements)

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“…Its alkylated molecules, alkylguanidines, are strong non-ionic organic bases with base strengths that are comparable to sodium hydroxide and the capability to catalyze liquid phase organic reactions such as methylation of phenol [109], Michael addition [110], alkylation of carboxylic acids [111] and transesterification [112][113][114][115][116][117]. Schuchardt and colleagues published several studies related to the application of alkylguanidine for the transesterification of triglyceride [112,113,116].…”

Section: Organic Solid Basesmentioning

confidence: 99%

Heterogeneous Base Catalysts for Transesterification in Biodiesel Synthesis

2009

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The heterogeneous base-catalyzed transesterification for biodiesel synthesis has been studied intensively over the last decade. This review classifies the solid base catalysts for transesterification into the following six categories based on Hattori's classification: single metal oxides, mixed metal oxides, zeolites, supported alkali/alkaline earth metals, clay minerals (hydrotalcites), and non-oxides (organic solid bases). The catalysts in each category have acceptable catalytic activities overall, and follow specific catalyst design rules, although not completely systematically, thereby drawing the best activity from them. In parallel, each catalyst is not versatile and has some limitations specifically related to its catalytic structure and properties. This review focuses on the heterogeneous base-catalyzed transesterification in terms of catalyst development, based on the published research, especially over the last decade.

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Section: Organic Solid Basesmentioning

confidence: 99%

Heterogeneous Base Catalysts for Transesterification in Biodiesel Synthesis

2009

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“…for C13HllN03: C 68. 1, H 4.8, N 6.1%; found: C 67.9, H 4.85, N 6.15. General method for the preparation of esters [6][7][8][9][10] A solution of the appropriate oxalic acid diester (0.005) mol) in dry ether (10 mL) was added to potassium ethoxide (0.01 mol from potassium (0.4 g) and ethanol (1.8 mL) in dry ether (20 mL)). A solution of the4-methylquinoline (0.005 mol) in dry ether (10 mL) was added dropwise and the mixture stirred for 3 days and allowed to stand for 4 days.…”

Section: I-(4-quinolyljpropan-2-one ( I )mentioning

confidence: 99%

Tautomerism in ketomethyl quinolines. Part 3. 4-Ketomethylquinolines

Greenhill¹,

Loghmani-Khouzani²,

Maitland³

1991

Can. J. Chem.

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. 69,696 (1991).A series of 4-ketomethylquinolines has been prepared and their tautomerism investigated. The compounds were prepared from 4-methylquinoline deprotonated with lithium diisopropylamide or potassium ethoxide and treated with esters. Attempted deprotonation with tert-butyllithium or phenyllithium led to 2-substituted-4-methylquinolines. The simple alkyl or aryl4-ketornethylquinolines exist essentially as the keto forms, but the quinoline-4-pyruvates are exclusively or substantially in the en01 forms.Key words: ketomethyl quinolines, pyruvates, tautornerism, enols. Chem. 69, 696 (1991).On a prCparC une sCrie de 4-~Ctom~thylquinol~ines et on a examink leur tautornkrie. On a prCparC les produits h partir de la 4-mCthylquinolCine dCprotonCe, ? i l'aide du diisopropylamide de lithium ou de 1'Cthylate de potassium, qui a Ct C traitCe par des esters. Des essais de dCprotonation a I'aide du tert-butyllithium ou le phtnyllithium ont conduit h la formation de 4-mCthylquinolkines substitutes en position 2. Les 4-~CtomtthylquinolCines portant des groupements aryles ou alkyles simples existent essentiellernent sous la forme cttonique; toutefois, les quinolCine-4-pyruvates existent exclusivernent ou presque sous la forme Cnolique.Mots cle's : ~CtomCthylquinolCines, pyruvates, tautornkrie, enols.[Traduit par la rCdaction] Introduction We recently conducted detailed investigations into the tautomerism of 2-ketomethylquinolines (I), Scheme 1. By a combination of ir and nrnr spectroscopy it was clearly shown that the enaminone form B was strongly favoured over the ketone form A for 2-ketomethylquinolines where R' = H, CN, or COOEt (R2 = alkyl, aryl, CN, COOEt, etc.). For the compounds with R1 = H, R2 = Me, Et, i-Pr, or t-Bu, the tautomeric mixtures in chloroform had 12-20% of the ketone forms and signals for both forms A and B could clearly be seen in the ir and the 'H, 13c, and 15N nmr spectra. The rest of the structures investigated showed only the enaminone signals. However, compounds of Scheme 1 where R1 = Me or Br were found to be exclusively in the ketone form A.

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“…We also developed a new route to higher-order guani-dine superbases since traditional approaches involving chloroformamidinium 16 or thiouronium 17 salts were consistently problematic in our hands. Compared to these electrophiles, carbonimidic dichloride 18 5 provided a more desirable balance of reactivity with nucleophiles and ease of handling.…”

Section: Synthesismentioning

confidence: 99%

Higher-Order Cyclopropenimine Superbases: Direct Neutral Brønsted Base Catalyzed Michael Reactions with α-Aryl Esters

Nacsa

Lambert

2015

J. Am. Chem. Soc.

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The synthesis and characterization of six new classes of higher-order superbases, including five that incorporate cyclopropenimine functionality, has been achieved. We propose a nomenclature that designates these as the CG2, GC2, PC3, PC1, C3, and GP2 classes of superbases. The pKBH+ values were measured to be between 29.0 and 35.6 in acetonitrile. Linear correlations of ten superbase basicities vs. that of their substituents demonstrated the insulating effect of the cyclopropenimine core. The molecular structures of several of these materials were obtained by single-crystal X-ray analysis, revealing interesting aspects of conformational bias and noncovalent organization. The types of superbasic cores and substituents were each shown reliably to affect selectivity for deprotonation over alkylation. Higher-order cyclopropenimine and guanidine superbase stability to hydrolysis was found to correlate to basicity. Finally, a GC2 base was found to catalyze conjugate additions of α-aryl ester pronucleophiles, representing the first report of a neutral Brønsted base to catalyze such reactions.

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Synthesis and properties of a series of sterically hindered guanidine bases

Cited by 119 publications

References 1 publication

Heterogeneous Base Catalysts for Transesterification in Biodiesel Synthesis

Heterogeneous Base Catalysts for Transesterification in Biodiesel Synthesis

Tautomerism in ketomethyl quinolines. Part 3. 4-Ketomethylquinolines

Higher-Order Cyclopropenimine Superbases: Direct Neutral Brønsted Base Catalyzed Michael Reactions with α-Aryl Esters

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