Abstract

Primary and N-alkyl arylamine motifs are key functional groups in pharmaceuticals, agrochemicals, and functional materials, as well as in bioactive natural products. However, there is a dearth of generally applicable methods for the direct replacement of aryl hydrogens with NH₂/NH(alkyl) moieties. Here, we present a mild dirhodium-catalyzed C-H amination for conversion of structurally diverse monocyclic and fused aromatics to the corresponding primary and N-alkyl arylamines using NH₂/NH(alkyl)-O-(sulfonyl)hydroxylamines as aminating agents; the relatively weak RSO₂O-N bond functions as an internal oxidant. The methodology is operationally simple, scalable, and fast at or below ambient temperature, furnishing arylamines in moderate-to-good yields and with good regioselectivity. It can be readily extended to the synthesis of fused N-heterocycles.

Unadorned Aziridines

Multiple catalytic methods have been developed to make aziridines—strained triangular carbon-nitrogen-carbon rings that function as versatile synthetic intermediates. However, the majority require protection of the nitrogen precursor with a sulfonyl group that is subsequently inconvenient to remove. Jat et al. (p. 61; see the Perspective by Türkmen and Aggarwal) used a hydroxylamine derivative as the nitrogen source together with an established rhodium catalyst to prepare a wide range of unprotected aziridines, with nitrogen bonded simply to hydrogen or a methyl group.

Abstract

New ketene equivalents, namely α-haloenol acetates, are investigated as both nucleophilic and electrophilic reactants in a tandem aldol–lactonization reaction. Diethylaluminum ethoxide proves to be an efficient promoter for the aldol reaction with a wide range of substrates, including inter alia, aldehydes, ketones, imines, nitrones and oximes, leading to oxetan-2-ones, azetidin-2-ones and isoxazolidin-5-ones. The resultant heterocyclic adducts are common structural elements in numerous compounds of interest as well as key intermediates in the preparation of other functionalities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

On the same route: Chromium-carbyne complexes are readily prepared by treatment of 1,1,1-trichloromethyl reagents with chromium(II) chloride. They serve as intermediates in the selective formation of a wide variety of products, such as alkynes, alkenes, β-hydroxy ketones, aldehydes, allylic alcohols, and allenes (see scheme, E=electrophile).

Detektivarbeit: FR252921, ein ungewöhnliches 19-gliedriges Lacton-Dilactam, und drei seiner Diastereomere wurden mit einer konvergenten Strategie aus drei Schlüsselsegmenten hergestellt (siehe Schema). Der Vergleich der synthetisierten Verbindungen mit dem natürlichen Material ergab eindeutig, dass FR252921 die Konfiguration 12S,13R,18R hat.

Auf gleichem Wege: Chrom-Carbin-Komplexe sind durch Umsetzung von 1,1,1-Trichlormethylreagentien mit Chrom(II)-chlorid leicht zugänglich und dienen als Intermediate zur selektiven Bildung unterschiedlichster Produktarten. Hierzu gehören Alkine, Alkene, β-Hydroxyketone, Aldehyde, Allylalkohole und Allene (siehe Schema, E=Elektrophil).

Synthetic detective work: FR252921, an unusual 19-membered lactone–dilactam, and three of its diastereomers were prepared by a versatile, convergent strategy from three key segments (see scheme). Comparison of the synthetic compounds with natural material established conclusively that FR252921 has the configuration 12S,13R,18R.

Deuterated arachidonic acid and 20-HETE were prepared in good overall yields and high stereoselectivities. Key transformations include a trans-specific vinyl dibromide reduction and Suzuki cross-couplings to a lithium borate or a 9-BBN borane. These standards are three and two mass units higher, respectively, than their naturally occurring counterparts and are useful in mass spectrometry analysis. Copyright © 2006 John Wiley & Sons, Ltd.

Die Reduktion von Trihalogenmethylcarbinolen 1 mit CrCl₂ liefert in guten bis ausgezeichneten Ausbeuten (Z)-α-Halogen-Enolester 2 und (Z)-β-Halogen-Enolether 3 durch Acyl- bzw. Wasserstoffwanderung. An der Reaktion ist vermutlich eine regio- und stereoselektive Umlagerung eines Chrom(III)-Fischer-Carbens beteiligt. R²=H, Alkyl, Aryl; X=F, Cl, Br.

Reduction of trihalomethylcarbinols 1 with CrCl₂ affords good to excellent yields of (Z)-α-haloenol esters 2 and (Z)-β-haloenol ethers 3 through acyl or hydrogen migration, respectively. The reaction is proposed to proceed through regio- and stereoselective rearrangement of a chromium(III) Fischer carbene. (R²=H, alkyl, aryl; X=F, Cl, Br).