The distribution of distances from atoms of a particular element E to a probe atom X (oxygen in most cases), both bonded and intermolecular non-bonded contacts, has been analyzed. In general, the distribution is characterized by a maximum at short E⋯X distances corresponding to chemical bonds, followed by a range of unpopulated distances – the van der Waals gap – and a second maximum at longer distances – the van der Waals peak – superimposed on a random distribution function that roughly follows a d3 dependence. The analysis of more than five million interatomic “non-bonded” distances has led to the proposal of a consistent set of van der Waals radii for most naturally occurring elements, and its applicability to other element pairs has been tested for a set of more than three million data, all of them compared to over one million bond distances.

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A cartography of the van der Waals territories

Department of Chemistry, Tianjin University, Tianjin 300072, China; Department of Applied Chemistry, China Agricultural University, Beijing 100193, China; UMR 6014 CNRS, Laboratoire COBRA de l’IRCOF, Université et INSA de Rouen, Rue Tesniere, F-76130 Mont Saint Aignan, France; and Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Science, Shanghai 200032, China

Asymmetric construction of stereogenic carbon centers featuring a trifluoromethyl group from prochiral trifluoromethylated substrates.

2.1.5. Electrophilic Attack on CdC 3994 2.1.6. NH Insertions in Diazo Compounds 3994 2.1.7. Pd Catalyzed Cyclizations 3994 2.2. Cyclizations by C-C Bond formation 3995 2.2.1. Nucleophilic Displacement of Halides 3995 2.2.2. Cyclizations Involving CdO Group 3995 2.3. Cycloadditions 3996 2.4. Ring Rearrangements 3997 2.4.1. Rearrangements of Four-Membered Rings 3997 2.4.2. Rearrangements of Larger Rings 3998 2.5. Reduction of Azetidin-2-ones 3998 2.6. Miscellaneous Syntheses 3999 2.7. Important Classes of Compounds 4000 2.7.1. Natural Products 4000 2.7.2. Azetidine Carboxylic Acids 4001 2.7.3. Exomethylene Azetidines 4002 2.7.4. Ligands for Metal-Catalyzed Reactions and Chiral Auxiliaries 4003

Novel syntheses of azetidines and azetidinones.

Asymmetric Strecker Reactions

Fishing for complements! There is an alternative to the useful Fischer indole synthesis. The new method utilizes the same retrosynthetic disconnection but is based on a Rh(III) -catalyzed directed CH activation step and a successive coupling with alkynes.

Indole synthesis by rhodium(III)-catalyzed hydrazine-directed C-H activation: redox-neutral and traceless by N-N bond cleavage.

Organocatalytic Conjugate Addition of Formaldehyde N,N-Dialkylhydrazones to β,γ-Unsaturated α-Keto Esters

The dual activation of α-keto esters and formaldehyde tert-butyl hydrazone by BINAM-derived bis-ureas is the key to achieve high reactivity and excellent enantioselectivities in nucleophilic addition (formal carbonyl-ene reaction) to functionalized tertiary carbinols. Ensuing high-yielding diazene-to-aldehyde tranformations and subsequent derivatizations provides a direct entry to a variety of densely functionalized products.

Asymmetric formal carbonyl-ene reactions of formaldehyde tert-butyl hydrazone with α-keto esters: dual activation by bis-urea catalysts.

N,N-Dialkylhydrazones as the Imine Component in the Staudinger-Like [2+2] Cycloaddition to Benzyloxyketene We thank the Dirección General de Investigación Científica y Técnica (grants BQU 2001-2376 and PPQ 2000-1341) and the Junta de Andalucía for financial support. We also thank the Ministerio de Educación y Ciencia for a doctoral fellowship to A.F.

The selective N-oxidation of the most nucleophilic amino nitrogen atom in hydrazides is central to the development of an unprecedented methodology for the cleavage of their N[bond]N bonds under oxidative conditions. Treatment of a series of hydrazides 1-9 with peracids such as magnesium monoperoxyphtalate hexahydrate (MMPP.6 H(2)O) or meta-chloroperbenzoic acid (m-CPBA) afforded the corresponding amides 10-16 in good-to-excellent yields (80-92 %). The extension of the methodology to carbamate-like substrates such as 17 and 18 was also investigated, but in this case the process is synthetically useless in view of the low yields observed of carbamates 19 and 20 (approximately 15 %). Experiments carried out with equivalent amounts of oxidant produced nitrones, such as 26, proceeding from the dialkylamino moiety, and (1)H NMR experiments indicated that this product is formed by fast conversion of the parent hydrazide, without detection of the expected hydrazide N-oxides. In addition, the over oxidation of 26 into nitronate 25 proceeds through an unknown intermediate. This oxidative N[bond]N bond cleavage by peracids is an alternative method for the deamination of hydrazides, and constitutes the only solution compatible with substrates carrying functionalities sensitive to reducing conditions.

Eloísa Martín-Zamora

Papers

Organocatalytic Conjugate Addition of Formaldehyde N,N-Dialkylhydrazones to β,γ-Unsaturated α-Keto Esters

Asymmetric formal carbonyl-ene reactions of formaldehyde tert-butyl hydrazone with α-keto esters: dual activation by bis-urea catalysts.

A Practical Oxidative Method for the Cleavage of Hydrazide N ? N Bonds

N,N-dialkylhydrazones as the imine component in the Staudinger-like [2+2] cycloaddition to benzyloxyketene.