Guanidine Base Research Articles

Highly Stereoselective [4+2] Cycloaddition of Azlactones to β,γ‐Unsaturated α‐Ketoesters Catalyzed by an Axially Chiral Guanidine Base

Sweet catalysis! The enantio- and diastereoselective cycloaddition reaction of azlactones with β,γ-unsaturated α-ketoesters was demonstrated by taking advantage of the multiple reactive sites on the azlactone with the use of an axially chiral guanidine-base catalyst. The most likely reaction pathway involves three consecutive steps to provide a facile access to α-amino δ-lactones with a sugar framework in a highly stereoselective manner (see scheme).

Transesterification of soybean oil on guanidine base-functionalized SBA-15 catalysts

SBA-15 functionalization with the guanidine base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was used to prepare TBD-grafted catalysts for the soybean oil transesterification reaction. The structural and textural features of both the support and the catalysts were investigated by X-ray diffraction, transmission electron microscopy, and nitrogen physisorption. CHN analysis and FTIR characterization were also carried out on the catalysts before and after reaction. Potentiometric titration was also used to confirm CHN analysis data for the fresh catalysts. Mild conditions (atmospheric pressure and 343K) were chosen for catalytic testing in a batch reactor. The influence of the base content and the reaction time on the methyl esters yield was investigated. All the catalysts were found active for the soybean oil conversion. Comparison with the catalytic behaviour of a commercial TBD-grafted polymer showed a superior performance of the functionalized SBA-15 catalysts. The higher the functionalization extent, the higher the activity, just a few hours being required for a 100mol% methyl esters yield. Over such a short reaction time leaching was observed to occur only to an extremely low extent, which makes possible to reuse the catalysts after a regeneration step consisting in a simple NaOH treatment of the recovered samples. During such treatment the catalyst base sites – poisoned (through protonation) by the free fatty acids – are freed, and their activity is restored.

Response to comment on “The interaction of cells and bacteria with surfaces structures at the nanoscale”

A UV photoinduced cross-linking of non-modified commercial poly(disulfide) resins (Thioplast) is reported via the air oxidative photocoupling of terminal thiol functions. Catalyzed by a photogenerated guanidine base (TBD), this step-growth photopolymerization is useful to maximize disulfide functions content. The mechanism proceeds through thiol deprotonation into thiolate anions, further oxidized into thiyl radicals, eventually dimerizing into disulfide cross-links. Starting with a detailed structural characterization of the thiol-terminated resin, photooxidative kinetics are studied under exposure to a polychromatic medium-pressure Hg arc using Raman and infrared spectroscopy. The effects of irradiance, film thickness, photobase concentration, resin molar mass, and content of an additional polythiol monomer (reactive diluent) have been investigated. In an effort of upscaling, irradiation under a 365 nm LED panel has enabled the fast preparation of 1.5 μm thick cross-linked poly(disulfide) coatings in a matter of minutes. Capitalizing on the ability of residual thiol groups to react with silver cations, a post-functionalization has been successfully performed, leading to films exhibiting at their surface stable thiolate-silver bonds as proved by X-ray photoelectron spectroscopy. Despite the well-established biocide action of silver ions, no antibacterial action has been evidenced by confocal fluorescence microscopy because of insufficient release.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) an efficient homogeneous catalyst for aldol condensation reactions. Study of the catalyst recovery and reusability using CO2

In this work it was shown that TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), a cheap and commercially available guanidine base, efficiently catalyzes aldol condensation reactions yielding interesting products for pharmacological and fragrance industries. This methodology works under solvent-less conditions and affords with very good conversions the corresponding products. Moreover, a simple and effective separation protocol using the CO2 fixation was employed. The catalyst could be recovered and re-used for three consecutive runs without significant loss of activity.

Anion Conducting Polyaromatics Having Guanidine Base

A guanidine based poly(arylene ether sulfone)s (PAES-TMG) membrane was synthesized from the poly(arylene ether sulfone)s having activated fluorine group and tetramethylguanidine (TMG) without chloromethylation and/or bromination. The methylated PAES-TMG membranes do not have β-hydrogen, and TMG groups have high basicity (pKa = 13.6), which may reduce the potential of degradation due to E2 and SN2 reaction. The membrane showed the good stability in alkaline conditions (0.5M NaOH boiling temperature for 2hr, 80oC for 382hr). The OH- conductivities before and after NaOH test at 80oC for 382hr are 0.036 S/cm, and 0.023S/cm, respectively. The conductivity after exposure to ambient air is 0.019S/cm (σHCO3-) at 80oC.

Anion Conducting Polyaromatics Having Guanidine Base

not Available.

Photo-induced crosslinking of water-soluble polymers with a new photobase generator

A strong bicyclic guanidine base, 1,5,7-triaza-bicyclo[4.4.0]dec-5-ene (TBD), is photo-generated from its tetraphenylborate salt (TBD·HBPh4) and can effectively catalyze the transesterification reaction between the ester and hydroxy groups in polymers. Accordingly, with TBD·HBPh4 as a photobase generator, a water-soluble polymer blend, namely poly(1-vinylpyrrolidone-co-2-dimethylaminoethyl methacrylate) and 2-hydroxyethyl cellulose, has been developed as a potential eco-friendly photoresist. This photoresist system uses only water as a solvent and as a developer, rather than organic solvents and aqueous alkaline developers. The effects of the amount of photobase generator, polymer composition and photolithographic conditions on the photo-induced crosslinking and patterning of water-soluble polymers were studied.

ChemInform Abstract: Guanidine Bases in Synthesis: Extending the Scope of the Corey—Chaykovsky Epoxidation

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Asymmetric Direct Vinylogous Aldol Reaction of Furanone Derivatives Catalyzed by an Axially Chiral Guanidine Base.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Enantioselective Electrophilic Amination of α‐Cyanothioacetates with Azodicarboxylates Catalyzed by an Axially Chiral Guanidine Base.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric Direct Vinylogous Aldol Reaction of Furanone Derivatives Catalyzed by an Axially Chiral Guanidine Base

Asymmetric Direct Vinylogous Aldol Reaction of Furanone Derivatives Catalyzed by an Axially Chiral Guanidine Base

Asymmetric Direct Vinylogous Aldol Reaction of Furanone Derivatives Catalyzed by an Axially Chiral Guanidine Base

Ace of Base: The first highly enantioselective direct vinylogous aldol reaction of dihalogenated or α-thio-substituted furanones with aldehydes utilizes an axially chiral guanidine base catalyst. The method provides facile access to enantioenriched γ-substituted butenolides.

Guanidine Bases in Synthesis: Extending the Scope of the Corey-Chaykovsky Epoxidation

Guanidine bases, such as 1,5,7-triazabicyclo[4.4.0]dec-1-ene (TBD) or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-1-ene (MTBD), are highly effective reagents for the in situ generation of sulfonium ylides from sulfonium salts in Corey-Chaykovsky epoxidation reactions of aldehydes. These reactions proceed rapidly to produce the corresponding epoxides in excellent yields and with high selectivity for the trans product. Significantly, this reagent combination is applicable to both nonenolizable and enolizable aldehydes and α,β-unsaturated aldehydes.

Catalytic Conjugate Additions of Geminal Bis(sulfone)s: Expanding the Chemistry of Sulfones as Simple Alkyl Anion Equivalents

The value of cyclic gem-bis(sulfone) 4 as a simple alkyl nucleophile equivalent in catalytic C-C bond-forming reactions is demonstrated. The 1,4-type nucleophilic additions of bis(sulfone) 4 to alpha,beta-unsaturated ketones take place by assistance of catalytic guanidine base. On the other hand, pyrrolidines are able to catalyze the conjugate addition of 4 to both enones and enals, likely by means of iminium ion activation. Upon exploration of the best chiral pyrrolidine catalyst, it has been found that the addition of 4 to enals catalyzed by diphenylprolinol silyl ether 10 proceeds with very high enantioselectivity (beta-aryl-substituted enals >95% ee; beta-alkyl substituted enals up to 94% ee; ee = enantiomeric excess). Further reductive desulfonation of adducts gives rise to the corresponding beta-methyl aldehydes, as well as the derived alcohols, acetals, and methyl esters after simple (Mg, MeOH) well-established protocols. Application of the procedure to the synthesis of biologically relevant phenethyl building blocks is shown. Most interestingly, alpha-alkylation of initially obtained bis(sulfone) adducts can be done even with less reactive alkylating reagents, such as long linear-chain or branched-chain alkyl halides. Accordingly, upon the desulfonation process, a general, experimentally simple and highly enantioselective access to beta-branched aldehydes, alcohols, or esters is possible. Further exploration of the method includes the use of chiral alpha,beta-unsaturated aldehydes derived from citronellal as the Michael acceptor partners. In these instances, the sense of the conjugate addition of 4 is controlled by the chirality of the pyrrolidine catalyst, thus allowing for a stereochemically predictable access to 1,3-dimethyl arrays, such as those present in deoxygenated polyketide-type natural products. The intramolecular variation of this technology by using doubly unsaturated aldehyde-ester 22 illustrated the site selectivity of the procedure and its potential for tandem processes leading to highly substituted polycyclic systems, such as 24.

Enantioselective Electrophilic Amination of α‐Cyanothioacetates with Azodicarboxylates Catalyzed by an Axially Chiral Guanidine Base

AbstractAn enantioselective electrophilic amination of α‐substituted cyanothioacetates with azodicarboxylate is demonstrated using an axially chiral guanidine as a chiral Brønsted base catalyst. The corresponding product, having a quaternary stereogenic center at the α‐carbon atom, is formed in excellent enantioselectivity.

ChemInform Abstract: Asymmetric Epoxidation of α,β‐Unsaturated Ketones with Hydrogen Peroxide Catalyzed by Axially Chiral Guanidine Base.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

CO2 -binding organic liquids (CO2 BOLs) for post-combustion CO2 capture

Abstract CO 2 -binding organic liquids (CO 2 BOLs) chemically bind and release CO 2 more efficiently than aqueous alkanolamine systems. CO 2 BOLs are comprised of alcohols and organic amidine or guanidine bases, which chemically bind CO 2 as liquid amidinium or guanidinium alkylcarbonate salts. CO 2 BOLs have high CO 2 binding capacities (19% by weight, 147 g CO 2 /L) compared to that of 30% monoethanolamine solution in water (7% by weight, 108 g CO 2 /L) because they are liquid with or without bound CO 2 and do not require any added solvent such as water. The dissolution of CO 2 into and out of the liquid phase limits the rate of CO 2 capture and release. Absorption of CO 2 is selective over nitrogen in both concentrated and dilute gas streams making these systems applicable to post- and pre-combustion CO 2 capture. The free energy of CO 2 binding in these systems is small and is independent of the choice of alcohol. The free energies of these systems are dependent on the choice of base; −9 kJ/mol for diazabicyclo[5.4.0]undec-7-ene (DBU) and Barton’s base and +2 kJ/mol for 1,1,3,3-tetramethylguanidine. The specific heats of the organic CO 2 BOLs are over 50% lower than that of water, resulting in a 50% reduction in the energy needed to strip out CO 2 as compared to aqueous alkanolamine solutions. CO 2 BOLs have been recycled for five cycles without losing activity or selectivity towards CO 2 .

Electron density controlled carbamate ligand binding mode: towards a better understanding of metalloenzyme activity

The first structurally characterized mononuclear biscarbamate complex of Zn with eta1-coordinated carbamate ligands can be prepared by reaction between [EtZn(O2CN(iBu)2)]4 and a guanidine base. Usage of a weaker base leads to eta2-coordinated complexes.

Asymmetric Epoxidation of a,b-Unsaturated Ketones with Hydrogen Peroxide Catalyzed by Axially Chiral Guanidine Base

The enantioselective epoxidation of α,β-unsaturated ketones with hydrogen peroxide was demonstrated using axially chiral guanidine as a base catalyst. Hydrogen peroxide can be utilized as a cost-effective and atom-efficient oxidant in the present catalytic epoxidation even under heterogeneous conditions. The newly developed axially chiral guanidine base bearing an additional central chirality functions as an efficient catalyst to provide epoxides in 51-65% ee.

An efficient, eco-friendly process for aldol and Michael reactions of trimethylsilyl enolate over organic base-functionalized SBA-15 catalysts

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD, a bicyclic guanidine base) functionalized SBA-15 was found to be an efficient catalyst for aldol reaction of trimethylsilyl enolate with aldehydes. Both aryl aldehydes and alkyl aldehydes provided aldol products in good yields. The applicability of this catalyst was extended to Michael reaction and in the synthesis of quaternary carbon. This novel heterogeneous catalyst offers several attractive advantages over soluble base catalysts such as high catalyst activity under mild reaction condition, easy recovery and reusability of the catalyst.