Xiaoyu Su

Copper-catalyzed decarboxylative cross-coupling of alkynyl carboxylic acids with aryl halides

The copper-catalyzed decarboxylative reactions of alkynyl carboxylic acids with aryl halides were performed under relatively mild reaction conditions. Benzofurans could be further prepared smoothly by a one-pot domino protocol on the basis of decarboxylative cross-coupling of 2-iodophenol.

Hydrolytic metalloenzyme models: Enantioselective hydrolysis of long chain α-amino acid esters by chiral metallomicelles composed of lipophilic l-histidinol

Abstract Chiral metallomicellar supramolecular systems composed of lipophilic l -histidinol have been investigated for their catalytic activities and enantioselectivities in the hydrolysis of N-protected α-amino acid esters. Kinetic evidence suggests that the mechanism of the deacylation promoted by ligand 4a with a hydroxyl group and 2a lacking a hydroxyl group is different. The apparent p K a of Zn 2+ - 4a is 6.8 in the micelllar aggregate. The highest enantioselectivity in hydrolysis of R ( S )-C 12 -Leu-PNP ( k S / k R =3.01) was obtained with 4a -Zn 2+ as catalyst.

Insight into the Role of the Counteranion of an Imidazolium Salt in Organocatalysis: A Combined Experimental and Computational Study

N-Heterocyclic carbenes (NHCs) can serve as very reactive nucleophilic catalysts and exhibit strong basicity. Herein, we initiate a combined experimental and computational investigation of the NHC-catalyzed ring-closing reactions of 4-(2-formylphenoxy)but-2-enoate derivatives 1 to uncover the relationship between the counteranion of an azolium salt, the nucleophilicity and basicity of the carbene species, and the catalytic performance of the carbene species by taking imidazolium salts IPr⋅HX (X=counteranion, IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as the representative precatalysts. The plausible mechanisms of IPr-mediated ring-closing reactions have been investigated by using DFT calculations. The hydrogen-accepting ability, assigned as the basicity of the counteranion of IPr⋅HX and evaluated by DFT calculations, is correlated with the rate of deprotonation of C2 in IPr⋅HX, which could be monitored by the capture of the free carbene formed in situ with elemental sulfur. The deprotonation of C2 in IPr⋅HX with a more basic anion gives rise to a higher concentration of the free carbene and vice versa. At a relatively low concentration, IPr prefers to show a nucleophilic character to induce the intramolecular Stetter reaction. At a relatively high concentration, IPr primarily acts as a base to afford benzofuran derivatives. These data comprehensively disclose, for the first time, that the counteranions of azolium salts significantly influence not only the catalytic activity, but also possibly the reaction mechanism.

Self-assembly of discrete homochiral, helical, hydrogen-bonded nanocages: from vesicles to microspheres and tubules capable of gelating solvents.

The chiral tris-monodentate imidazolinyl ligands 1 a-c exhibit a strong tendency to form the discrete, helical [2+3] nanocages 3 ([1(2).2(3)]) with tartaric acids 2. Circular dichroism (CD) spectra and theoretical calculations reveal that supramolecular handedness of capsulelike architectures is determined only by the chirality of the imidazolinyl ligands rather than tartaric acids. The chirality of imidazolinyl ligands is transferred to the helicity of the complexes through the directed hydrogen bonds between the N3 atom of imidazoline rings and the carboxyl of tartaric acids. These hydrogen-bonded nanocages can spontaneously self-assemble into spherical vesicles, during which the hydrogen bonding that arises from the hydroxyl groups of tartaric acids plays a crucial issue. The vesicles formed by [{(S,S,S)-1 a}(2)(2(L))(3)] (3 a) may further evolve into microspheres that gelate organic solvents after being aged at -20 degrees C for 24 h, and can also be unprecedentedly transformed to tubular assemblies capable of rigidifying the solvents when subjected to ultrasound irradiation.

Enantioselective recognitions of chiral molecular tweezers containing imidazoliums for amino acids

Two kinds of novel chiral molecular tweezers containing imidazoliums were synthesized from L-alanine, L-phenylalanine, and L-glutamic acid. They are constructed by the chiral imidazolium pincers and two different spacers which are 1,3-bis (bromomethyl)benzene and 2,6-bis(bromomethyl)pyridine, respectively. The enantioselective recognition of L- and D-amino acid derivatives by these molecular tweezers was investigated by UV spectroscopic titration experiments and good enantioselectivities were obtained, which are highly sensitive to whether the spacer has the binding site and the pincers has the other aromatic rings besides imidazolium ring. The host molecular 3b.2PF6- showed remarkable enantioselectivity for N-Boc protected histidine methyl ester, affording K(L)/K(D) of 5.10.

1,4-Bis(imidazol-1-yl)benzene-terephthalic acid (1/1).

In the title compound, C12H10N4·C8H6O4, 1,4-bis(imidazol-1-yl)benzene and terephthalic acid molecules are joined via strong O—H⋯N hydrogen bonds to form infinite zigzag chains. Both molecules are located on crystallographic inversion centers. The O—H⋯N hydrogen-bonded chains are assembled into two-dimensional layers through weak C—H⋯O and strong π–π stacking interactions [centroid–centroid distance = 3.818 (2) Å], leading to the formation of a three-dimensional supramolecular structure.