The N-carbamoyl squaramide dimer: a compact, strongly associated H-bonding motif

Davis, Anthony P.; Draper, Sylvia M.; Dunne, Gavin; Ashton, Peter R.

doi:10.1039/a907179b

Cited by 45 publications

(39 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Spectrophotometric titrations: All titrations were performed at 25 8C. For the determination of binding constants in acetonitrile, the solution of receptor (1)(2)(3)(4)(5) was titrated with a 100-fold more concentrated solution of the anion as the TBA + salt. After each addition of a sub-stoichiometric amount of anion, the UV/Vis spectrum was recorded.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Urea‐, Squaramide‐, and Sulfonamide‐Based Anion Receptors: A Thermodynamic Study

Amendola

Fabbrizzi

Mosca

et al. 2011

Chemistry A European J

104

View full text Add to dashboard Cite

In this work, we compare the anion-binding capabilities of receptors 1-5, characterized by similar structures, but possessing different hydrogen-bond-donor moieties (urea, squaramide, and sulfonamide). The presence of chromophoric substituents on the receptor's skeleton allowed the determination of association constants by performing UV/Vis titrations with the investigated anions on solutions of the receptors in pure acetonitrile. Additional quantitative studies of the anion-binding properties of receptors 1-5 were performed by isothermal titration calorimetry (ITC). The experimental results indicated that 1 and 2 formed 1:1 hydrogen-bonded complexes with most of the anions investigated. In the case of receptors 3-5, the formation of the 1:1 adduct was observed only with anions of low basicity (i.e., chloride, bromide, iodide, and hydrogen sulfate). With more basic anions (i.e., acetate and dihydrogen phosphate), both spectrophotometric and ITC titrations accounted for the deprotonation of the sulfonamide group, involving the formation of the conjugated base of the receptor.

show abstract

Section: Methodsmentioning

confidence: 99%

“…Higher selectivity can be achieved by placing the donor groups around the cavity of macrocycles [5] or cage-shaped receptors. [6] The hydrogen-bond donor ability of NÀH groups can be further increased by introducing electron-withdrawing substituents on the receptor framework.…”

Section: Introductionmentioning

confidence: 99%

Urea‐, Squaramide‐, and Sulfonamide‐Based Anion Receptors: A Thermodynamic Study

Amendola

Fabbrizzi

Mosca

et al. 2011

Chemistry A European J

104

View full text Add to dashboard Cite

show abstract

“…The squaramide-functional group has recently been exploited in supramolecular chemistry for the design of anion receptors (13)(14)(15)(16)(17)(18), self-complementary molecularrecognition motifs (19) and, most recently, by Gale and coworkers (20) where the squaramide motif was found to be a potent functionality for transmembrane anion transport of both chloride and bicarbonate. Notably, previous work indicates that the introduction of electron-withdrawing trifluoromethyl groups onto the squaramide aromatic substituents can be used to modify both lipophilicity and anion-binding affinity (10,13).…”

Section: Introductionmentioning

confidence: 99%

Amino acid-based squaramides for anion recognition

Elmes

Jolliffe

2014

Supramolecular Chemistry

View full text Add to dashboard Cite

Eight receptors 1 -8 comprising an L-lysine scaffold modified at N-and C-termini with aliphatic alkyl chains and N,N 0 -alkyl amides, respectively, and bearing squaramide moieties on the amino acid side chain were synthesised by a combination of solid-and solution-phase chemistries and shown to complex various anions in 0.5% H 2 O in dimethyl sulfoxide-d 6 solution. All of the receptors were found to bind SO 22 4 ; Cl 2 , AcO 2 and BzO 2 via hydrogen-bond or acid -base interactions with the squaramide protons; however, 1 was found to bind to SO 22 4 via hydrogen bonds formed between the anion and both the squaramide and amide NH moieties. Moreover, modification of both the N-and C-termini of the amino acids with different alkyl substituents had a negligible effect on their anion-binding properties while simultaneously conferring lipophilicities in a range that is optimal for molecules to behave as 'drug-like' systems as defined by Lipinski's rule of five. The results of this study demonstrate the versatility of such amino acid receptors as building blocks in the field of anion recognition.

show abstract

“…Next, we examined the effect of catalyst loading and concentration of the substrates. Reducing the catalyst loading from 5 mol% to 2 mol% or 1 mol% resulted in a lower enantioselectivities (entries [10][11][12]. Furthermore, it was observed that the enantiomeric excess of 4a generally decreased on raising the concentration of the substrate from 0.125 mmol/L to 0.5 mmol/L (entries 9, 13 and 14).…”

mentioning

confidence: 98%

“…Although the reaction gave us higher yield (65% compare with 48%), only 37% ee was obtained (entry 15). Based on our experience and Davis' work, 10 we speculated that the squaramide catalysts may exist in solvent as oligomer and should be deaggregated by interacting with substrate. Lower temperature could strengthen the self-interaction of squaramide and lead to a loss in stereocontrol of reaction.…”

mentioning

confidence: 98%

Direct Bifunctional Squaramide-Catalyzed Asymmetric N-Nitroso Aldol Reaction of Tertiary β-Carbonyl Esters

Yang¹,

Dai²,

Yang³

et al. 2012

Synlett

View full text Add to dashboard Cite

N -N i t r o s o A l d o l R e a c t i o n o f T e r t i a r y b -C a r b o n y l E s t e r s w i t h S q u a r a m i d e C a t a l y s t s SYNLETT 2012, 23, 948-950x x . x x . 2 0 1 2 Advanced online publication: 15.03.2012 Abstract: Enantioselective asymmetric N-nitroso aldol reaction of tertiary b-carbonyl esters using the bifunctional squaramide organanocatalysts is described. These adducts have been obtained in moderate yields and with up to 98% ee.Key words: N-nitroso aldol reaction, bifunctional squaramide catalysts, asymmetric catalysis, b-carbonyl esters, nitrosobenzene Asymmetric N-nitroso aldol reaction is a powerful synthetic tool for the expedient formation of C-N bond, which can be used to construct optically active a-hydroxyamino carbonyl compounds. 1 The enantioselective catalytic version of N-nitroso aldol reaction was pioneered in 2003 by Yamamoto et al. using a chiral silver complex as catalyst. 2 This seminal work was later followed up by the excellent studies of Yoshida 3 and others. 4 Among them, significant advances have been made in the improvement to the reaction using metal-based catalytic systems. Although, thus far, several organocatalytic a-hydroxyamination reactions of aldehydes, ketones and isolated enolate precursors have been achieved using chiral secondary amines 5 or TADDOL derivatives 6 as the catalyst, enantioselective constructions of quaternary stereocenters by the direct N-nitroso aldol reaction are rare. 4b,7 Jørgensen 7a et al. and Chen 7b et al. reported cinchona alkaloid derivatives promoted a-hydroxyamination of tertiary esters and lactams, respectively, and only gave enantioselectivities ranging from 22 to 72%.Recently, our group and others reported a series of investigation on chiral squaramide derivatives promoted enantioselective organic transformations. 8 We reasoned that the reaction substrates, like nitrosobenzene and b-carbonyl esters, could be activated via the hydrogen-bonding interaction with squaramide moiety and deprotonation by the neighboring tertiary amino group. Herein we present a direct enantioselective a-hydroxyamination of tertiary bcarbonyl esters catalyzed by chiral squaramide catalysts.The reaction of ethyl 2-oxocyclopentanecarboxylate and nitrosobenzene was selected as a model. We screened the reaction conditions including: catalysts, temperature, solvents, and concentrations of substrate. The results are summarized in Table 1. All four chiral catalysts were synthesized according to the methods described before by our laboratory 8j and other groups. 9,8b,d In these catalysts, 3a-c bearing both a tertiary amine moiety and a squaramide or thiourea within the same molecule can be easily prepared by condensation of a chiral amine and a monosubstituted squaric ester or isothiocyanate, and 3d contains a squaramide linked to two quinine amine groups. The structure of these catalysts is shown in Figure 1. In an initial screening of catalysts, we found that 3a was an excellent catalyst for the model reaction and gave the corresponding a-hydroxyamino...

show abstract

The N-carbamoyl squaramide dimer: a compact, strongly associated H-bonding motif

Cited by 45 publications

References 8 publications

Urea‐, Squaramide‐, and Sulfonamide‐Based Anion Receptors: A Thermodynamic Study

Urea‐, Squaramide‐, and Sulfonamide‐Based Anion Receptors: A Thermodynamic Study

Amino acid-based squaramides for anion recognition

Direct Bifunctional Squaramide-Catalyzed Asymmetric N-Nitroso Aldol Reaction of Tertiary β-Carbonyl Esters

Contact Info

Product

Resources

About