Small-molecule H-bond donors in asymmetric catalysis.

Asymmetric 1,3-Dipolar Cycloaddition Reactions

Huisgen's 1,3-dipolar cycloadditions become nonconcerted when copper(I) acetylides react with azides and nitrile oxides, providing ready access to 1,4-disubstituted 1,2,3-triazoles and 3,4-disubstituted isoxazoles, respectively. The process is highly reliable and exhibits an unusually wide scope with respect to both components. Computational studies revealed a stepwise mechanism involving unprecedented metallacycle intermediates, which appear to be common for a variety of dipoles.

Copper(I)-catalyzed synthesis of azoles. DFT study predicts unprecedented reactivity and intermediates.

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.

Asymmetric multicomponent reactions (amcrs): the new frontier

140 years ago Adolf von Baeyer proposed the structure of a heteroaromatic compound which revolutionized organic and medical chemistry: indole. After more than a century, indole itself and the complexity of naturally occurring indole derivatives continue to inspire and influence developments in synthetic chemistry. In particular, the ubiquitous presence of indole rings in pharmaceuticals, agrochemicals, and functional materials are testament to the ever increasing interest in the design of mild and efficient synthetic routes to functionalized indole derivatives. This Review emphasizes the achievements in the selective catalytic functionalization of indoles (C-C bond-forming processes) over the last four years.

Catalytic Functionalization of Indoles in a New Dimension

Enantioselective α-Amination of Ketones Mediated by Chiral Nitridomanganese(V) Complexes Using Ammonia as the Terminal Nitrogen Source.

R,2'S)-l'-Oxo-2,2'-spirobi(indan)-l-yl (1 S)-4, 7,7-trimethyl- 3 -oxo-2-oxabicyclo )hept- (1972). A stereoselective reduction of one of the carbonyl groups in the diketone was performed with lithium tri-tert-butoxylaluminium hydride. The resulting alcohol group in the racemic trans-hydroxy ketone was transformed into an ester by acylation with (-)-to-camphanic acid chloride conserving the geometry of the reduced carbon. The two diaster- eomeric esters formed, (1) and (2), were separated by fractional crystallization. (1) had lower solubility in acetone than (2) and was isolated as nice pure crys- tals in the first fractions. (2), with a lower melting point than (1), was more difficult to isolate, and had to be recrystallized several times to obtain a single crystal useful for X-ray analysis. Equidimensional single-crystal fragments of maxi- mum dimensions less than 0.5 mm were used for the crystallographic examinations. The space groups of both crystals were determined from precession photographs to be monoclinic with only systematic absences 0k0 for k odd indicating P21. The lattice constants of both compounds were refined from approximately 25 centred reflections in the range 20 30-(/) were used for structure determination and refinements. It was observed that intensities drop more quickly with sin0/a for (2) than for (1), and so for (2) data were collected for 20 _ 3o-(1). The intensities were corrected for Lorentz and polarization effects. /z(1) = 0.83 cm-i and /~(2) = 0.81 cm -~, thus no absorption corrections were applied. Positions of all C and O atoms in the structures were found by direct methods (Sheldrick, 1990). H-atom positions were found from difference Fourier maps. The structures were refined by full- matrix least-squares techniques using anisotropic thermal parameters for the non-H atoms and iso-

http://journals.iucr.org/c/issues/1993/06/00/ab1039/ab1039.pdf

Two structures involved in the separation of the enantiomeric pair of 2,2'-spirobi[indan]-1,1'-dione

Catalytic Enantioselective Addition of Aromatic Amines to Enones: Synthesis of Optically Active β-Amino Acid Derivatives.

Catalytic, Highly Enantioselective Friedel—Crafts Reactions of Aromatic and Heteroaromatic Compounds to Trifluoropyruvate. A Simple Approach for the Formation of Optically Active Aromatic and Heteroaromatic Hydroxy Trifluoromethyl Esters.

Rita G. Hazell

Papers

Enantioselective α-Amination of Ketones Mediated by Chiral Nitridomanganese(V) Complexes Using Ammonia as the Terminal Nitrogen Source.

Two structures involved in the separation of the enantiomeric pair of 2,2'-spirobi[indan]-1,1'-dione

Catalytic Enantioselective Addition of Aromatic Amines to Enones: Synthesis of Optically Active β-Amino Acid Derivatives.

Catalytic, Highly Enantioselective Friedel—Crafts Reactions of Aromatic and Heteroaromatic Compounds to Trifluoropyruvate. A Simple Approach for the Formation of Optically Active Aromatic and Heteroaromatic Hydroxy Trifluoromethyl Esters.

Rearrangement Reactions of Oxaziridines to Nitrones. X-Ray Crystal and Molecular Structure of N-tert.-Butyl-α(o-hydroxyphenyl)nitrone.