Dynamic NMR spectroscopy can determine energy barriers due to internal motion over the range of about 4.5-23 kcal mol -1 . Conformational analysis of the frozen conformations can be simulated and interpreted by reliable theoretical calculations based mainly on density functional theory (DFT). The same calculations can identify transition states

Ir(III) cationic complexes with cyclometalating tetrazolate ligands were prepared for the first time, following a two-step strategy based on (i) a silver-assisted cyclometalation reaction of a tetrazole derivative with IrCl3 affording a bis-cyclometalated solvato-complex P ([Ir(ptrz)2(CH3CN)2](+), Hptrz = 2-methyl-5-phenyl-2H-tetrazole); (ii) a substitution reaction with five neutral ancillary ligands to get [Ir(ptrz)2L](+), with L = 2,2'-bypiridine (1), 4,4'-di-tert-butyl-2,2'-bipyridine (2), 1,10-phenanthroline (3), and 2-(1-phenyl-1H-1,2,3-triazol-4-yl)pyridine (4), and [Ir(ptrz)2L2](+), with L = tert-butyl isocyanide (5). X-ray crystal structures of P, 2, and 3 were solved. Electrochemical and photophysical studies, along with density functional theory calculations, allowed a comprehensive rationalization of the electronic properties of 1-5. In acetonitrile at 298 K, complexes equipped with bipyridine or phenanthroline ancillary ligands (1-3) exhibit intense and structureless emission bands centered at around 540 nm, with metal-to-ligand and ligand-to-ligand charge transfer (MLCT/LLCT) character; their photoluminescence quantum yields (PLQYs) are in the range of 55-70%. By contrast, the luminescence band of 5 is weak, structured, and blue-shifted and is attributed to a ligand-centered (LC) triplet state of the tetrazolate cyclometalated ligand. The PLQY of 4 is extremely low (<0.1%) since its lowest level is a nonemissive triplet metal-centered ((3)MC) state. In rigid matrix at 77 K, all of the complexes exhibit intense luminescence. Ligands 1-3 are also strong emitters in solid matrices at room temperature (1% poly(methyl methacrylate) matrix and neat films), with PLQYs in the range of 27-70%. Good quality films of 2 could be obtained to make light-emitting electrochemical cells that emit bright green light and exhibit a maximum luminance of 310 cd m(-2). Tetrazolate cyclometalated ligands push the emission of Ir(III) complexes to the blue, when compared to pyrazolate or triazolate analogues. More generally, among the cationic Ir(III) complexes without fluorine substituents on the cyclometalated ligands, 1-3 exhibit the highest-energy MLCT/LLCT emission bands ever reported.

Dedicated to Professor Alfredo Ricci on the occasion of his 70th birthdayThe structural complexity and well-defined three-dimensional architecture of natural molecules are generally correlated with specificity of action and potentially useful biological properties.[1] This complexity has inspired generations of synthetic chemists to design novel enantioselective strategies for assembling challenging target structures and reproducing the rich structural diversity inherent in natural molecules. This symbiotic correlation between natural compounds synthesis and the discovery of effective asymmetric-generally catalytic [2] -technologies lies at the heart of the synthetic chemistry innovation.[3] Despite the substantial advances made thus far, the construction of highly strained polycyclic structures (particularly those that contain spiro-stereocenters) and the generation of all-carbon quaternary stereocenters still remain daunting targets for synthesis. [4,5] The spirocyclic oxindole core is featured in a number of natural products [6] as well as medicinally relevant compounds [7] (Figure 1), but its stereocontrolled synthesis, particularly installing the challenging spiro-quaternary stereocenter, poses a great synthetic problem. Only a few venerable asymmetric transformations, such as cycloaddition processes [8] or the intramolecular Heck reaction, [9] have proven suitable for achieving this challenging goal.Herein we show that asymmetric organocascade catalysis, [10] which exploits the ability of chiral amines to efficiently combine two modes of catalyst activation of carbonyl compounds (iminium and enamine catalysis) into one mechanism, [11] allows the direct, one-step synthesis of complex spirooxindolic cyclohexane derivatives; these products have three or four stereogenic carbon atoms and are obtained with extraordinary levels of stereocontrol starting from simple precursors. Specifically, we developed complementary organocatalytic multicomponent domino reactions based on two distinct organocatalysts, A and B, which efficiently activate carbonyl compounds such as ketones and aldehydes, respectively, toward multiple asymmetric transformations in a welldefined cascade sequence. Both strategies provide straightforward access to natural product inspired compound collections, [12] which would be difficult to synthesize by other enantioselective methods.

In spite of the many catalytic methodologies available for the asymmetric functionalization of carbonyl compounds at their α and β positions, little progress has been achieved in the enantioselective carbon–carbon bond formation γ to a carbonyl group. Here, we show that primary amine catalysis provides an efficient way to address this synthetic issue, promoting vinylogous nucleophilicity upon selective activation of unmodified cyclic α,β-unsaturated ketones. Specifically, we document the development of the unprecedented direct and vinylogous Michael addition of β-substituted cyclohexenone derivatives to nitroalkenes proceeding under dienamine catalysis. Besides enforcing high levels of diastereo- and enantioselectivity, chiral primary amine catalysts derived from natural cinchona alkaloids ensure complete γ-site selectivity: The resulting, highly functionalized vinylogous Michael adducts, having two stereocenters at the γ and δ positions, are synthesized with very high fidelity. Finally, we describe the extension of the dienamine catalysis-induced vinylogous nucleophilicity to the asymmetric γ-amination of cyclohexene carbaldehyde.

No abstract

The asymmetric Povarov reaction of N-arylimines with 2- and 3-vinylindoles has been developed using a chiral phosphoric acid ((S)-TRIP) as catalyst. The peculiar reactivity of vinylindoles allowed also the disclosure of a Povarov Friedel-Crafts sequence, and the trapping of the reaction intermediate with nucleophilic species, thus providing a versatile platform for the preparation of highly enantioenriched indole derivatives.

An outlook of the various research fields of organic chemistry where conformational analysis plays a fundamental role is presented. The section Methodologies for Conformational Analysis is focused on the information that can be obtained by various spectroscopic techniques such as nuclear magnetic resonance and optical methods such as electronic circular dichroism and vibrational circular dichroism. A comprehensive screening of the more recent ab initio and density functional theory theoretical approaches to conformational analysis is presented in the section Theoretical Conformational Analysis. The section Application of Conformational Analysis to the Determination of the AC of Organic Molecules shows how the synergic use of experimental and theoretical methods can solve challenging conformational tasks arising from modern organic chemistry. © 2011 John Wiley & Sons, Ltd. This article is categorized under: Electronic Structure Theory > Density Functional Theory

Electron-rich aromatic compounds such as 2-naphthol give a faster and asymmetric 1-aminoalkylation with high yields when treated with (R)-1-phenylethylamine and aromatic aldehydes in solvent-free conditions. An asymmetric transformation of a second kind, probably induced by the preferential crystallization of one diastereomer, affords the straightforward and stereoselective synthesis of aminoalkylnaphthols. Mechanisms predictable for this asymmetric reaction are reported. The absolute configurations and the conformations of the unknown aminonaphthols are widely ascertained.