Copper-catalyzed asymmetric 1,6-conjugate addition of in situ generated para-quinone methides with ß-ketoesters.

A Cu-catalyzed asymmetric 1,6-conjugate addition of in situ generated para-quinone methides (p-QMs) with ß-ketoester has been developed to construct a ketoester skeleton bearing an adjacent tertiary-quaternary carbon stereocenter in good yields and high enantioselectivities. This is the first example of metal-catalyzed asymmetric transformations of the in situ generated p-QMs, avoiding using pre-synthesized p-QMs requiring bulky 2,6-substitutions and highlighting a new dual catalytic activation with the chiral bis(oxazoline)-metal complex acting as a normal Lewis acid to activate the ß-ketoesters and a source of Brønsted acid responsible for generating the p-QMs in situ.

Novel Diketopyrrolopyrrole-Based π-Conjugated Molecules Synthesized Via One-Pot Direct Arylation Reaction.

Diketopyrrolopyrrole (DPP) is an important type of π-conjugated building block for high-performance organic electronic materials. DPP-based conjugated materials are usually synthesized via Suzuki, Stille, or Negishi cross-coupling reactions, which require organometallic precursors. In this paper, a series of novel phenyl-cored DPP molecules, including five meta-phenyl-cored molecules and four para-phenyl-cored molecules, have been synthesized in moderate to good yields, in a facile manner, through the Pd-catalyzed direct arylation of C-H bonds, and their optoelectrical properties have been investigated in detail. All new molecules have been fully characterized by NMR, MALDI-TOF MS, elemental analysis, UV-visible spectroscopy, and cyclic voltammetry. This synthetic strategy has evident advantages of atom- and step-economy and low cost, compared with traditional cross-coupling reactions.

Origin of anomeric effect: a density functional steric analysis.

The anomeric effect (the tendency of heteroatomic substituents adjacent to a heteroatom within the cyclohexane ring to prefer the axial orientation instead of the sterically less hindered equatorial position) is traditionally explained through either the dipole moment repulsion or the hyperconjugation effect. In this work, by employing our recent work in density functional steric analysis, we provide a novel two-component explanation, which is consistent with the common belief in chemistry that the effect has a stereoelectronic origin. With α-D-glucopyranose as the prototype, we systematically explore its conformational space and generate 32 isomers, leading to a total of 80 axial-equatorial conformation pairs. The energy difference analysis of these pairs shows that while statistically speaking the tendency is valid, the anomeric effect is not always true and can be violated. Three energy components, exchange-correlation, classical electrostatic, and density functional steric, are found to be directly proportional to the total energy difference between axial and equatorial isomers. We also found that the total dipole moment change, not the hyperconjugation effect, is a reasonable indicator of the total energy difference. However, all these correlations alone are not strong enough to provide a compellingly convincing explanation for the general validity of the effect. With the help of strong correlations between energy components, an explanation with two energy components, steric and electrostatic, was proposed in this work. We show that the axial-equatorial energy difference in general, with the anomeric effect as a special case, is dictated by two factors of the stereoelectronic origin, steric hindrance and classical electrostatic interactions, synchronously working together. Another explanation in terms of exchange-correlation and electrostatic interactions has also been obtained in this work.

Three new oligostilbenes from the seeds of Paeonia suffruticosa.

Three new oligostilbenes, trans-suffruticosol D (1), cis-suffruticosol D (2), and cis-gnetin H (7), were isolated along with the eight known stilbenes, trans-resveratrol (3), trans-epsilon-viniferin (4), cis-epsilon-viniferin (5), gnetin H (6), suffruticosol A (8), suffruticosol B (9), suffruticosol C (10), and cis-ampelopsin E (11) from the seeds of Paeonia suffruticosa. Compounds 3-6 were isolated for the first time from this plant species, and compound 11 was isolated for the first time from the genus Paeonia. The structures of the new compounds were elucidated based on spectral analyses, including 1D and 2D NMR experiments. The absolute configuration of compound 1 was determined by quantum chemical calculation of the electronic circular dichroism and comparison with the experimental circular dichroism spectrum.

One-pot organocatalytic asymmetric synthesis of 3-nitro-1,2-dihydroquinolines by a dual-activation protocol.

Generally, amine-catalyzed enantioselective transformations rely on chiral enamine or unsaturated iminium intermediates. Herein, we report a protocol involving dual activation by an aromatic iminium and hydrogen-bonding. An enantioselective aza-Michael-Henry domino reaction of 2-aminobenzaldehydes with nitroolefins has been developed through this protocol using primary amine thiourea catalysts to provide a variety of 3-nitro-1,2-dihydroquinolines in moderate yields and with up to 90% ee. The mechanism for the catalytic enantioselective reaction was confirmed by ESI mass spectrometric detection of the reaction intermediates. The products formed are substructures found in skeletons of important biological and pharmaceutical molecules.

N'-[(E)-2-Hydroxy-benzyl-idene]-5-methyl-isoxazole-4-carbohydrazide monohydrate.

In the structure of the title compound, C(12)H(11)N(3)O(3)·H(2)O, the dihedral angle formed by the benzene and isoxazole rings is 2.03 (8)°. The mol-ecular conformation is stabilized by an intra-molecular O-H⋯N hydrogen bond. In the crystal structure, mol-ecules are linked into a three-dimesional network by inter-molecular N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds, and by π-π stacking inter-actions involving adjacent benzene and isoxazole rings [centroid-centroid separation = 3.663 (2) Å].