C-H oxidation has a long history and an ongoing presence in research at the forefront of chemistry and interrelated fields. As such, numerous highly useful articles and reviews have been written on this subject. Logically, these are generally written from the perspective of the scope and limitations of the reagents employed. This Minireview instead attempts to emphasize chemoselectivity imposed by the nature of the substrate. Consequently, many landmark discoveries in the field of C-H oxidation are not discussed, but hopefully the perspective taken herein will allow C-H oxidation reactions to be more readily incorporated into synthetic planning.

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If C-H bonds could talk: selective C-H bond oxidation.

Conformational analysis—CI

From menthol to cholesterol to Taxol, terpenes are a ubiquitous group of molecules (over 55,000 members isolated so far) that have long provided humans with flavours, fragrances, hormones, medicines and even commercial products such as rubber. Although they possess a seemingly endless variety of architectural complexities, the biosynthesis of terpenes often occurs in a unified fashion as a 'two-phase' process. In the first phase (the cyclase phase), simple linear hydrocarbon phosphate building blocks are stitched together by means of 'prenyl coupling', followed by enzymatically controlled molecular cyclizations and rearrangements. In the second phase (the oxidase phase), oxidation of alkenes and carbon-hydrogen bonds results in a large array of structural diversity. Although organic chemists have made great progress in developing the logic needed for the cyclase phase of terpene synthesis, particularly in the area of polyene cyclizations, much remains to be learned if the oxidase phase is to be mimicked in the laboratory. Here we show how the logic of terpene biosynthesis has inspired the highly efficient and stereocontrolled syntheses of five oxidized members of the eudesmane family of terpenes in a modicum of steps by a series of simple carbocycle-forming reactions followed by multiple site-selective inter- and intramolecular carbon-hydrogen oxidations. This work establishes an intellectual framework in which to conceive the laboratory synthesis of other complex terpenes using a 'two-phase' approach.

Total synthesis of eudesmane terpenes by site-selective C–H oxidations

Die C-H-Oxidation hat eine lange Geschichte und ist seit jeher Teil der Spitzenforschung in der Chemie und verwandten Gebieten. Folgerichtig wurde bereits eine grose Zahl sehr nutzlicher Originalbeitrage und Ubersichten zu diesem Thema veroffentlicht. Logischerweise wurden diese Artikel im Allgemeinen mit Blick auf die Anwendungsmoglichkeiten und Grenzen der verwendeten Reagentien geschrieben. Ziel dieses Kurzaufsatzes ist es hingegen, stattdessen die durch die Eigenschaften der Substrate hervorgerufene Chemoselektivitat herauszuarbeiten. Dies bringt es mit sich, dass viele bahnbrechende Entdeckungen auf dem Gebiet der C-H-Oxidationen nicht behandelt werden; die hier eingenommene Sichtweise wird aber hoffentlich eine schnellere Aufnahme von C-H-Oxidationsreaktionen in Syntheseplanungen ermoglichen.

Wenn C‐H‐Bindungen sprechen könnten – selektive Oxidationen von C‐H‐Bindungen

The application of small molecules as catalysts for the diversification of natural product scaffolds is reviewed. Specifically, principles that relate to the selectivity challenges intrinsic to complex molecular scaffolds are summarized. The synthesis of analogues of natural products by this approach is then described as a quintessential “late-stage functionalization” exercise wherein natural products serve as the lead scaffolds. Given the historical application of enzymatic catalysts to the site-selective alteration of complex molecules, the focus of this Review is on the recent studies of nonenzymatic catalysts. Reactions involving hydroxyl group derivatization with a variety of electrophilic reagents are discussed. C–H bond functionalizations that lead to oxidations, aminations, and halogenations are also presented. Several examples of site-selective olefin functionalizations and C–C bond formations are also included. Numerous classes of natural products have been subjected to these studies of site-sel...

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Applications of Nonenzymatic Catalysts to the Alteration of Natural Products

Es wurden unter standardisierten Reaktionsbedingungen relative Geschwindigkeiten der Chromsaureoxydation verschiedener sekundarer Steroid-Alkohole bestimmt. In Ubereinstimmung mit einer von D. H. R. Barton ausgesprochenen Regel konnte dabei festgestellt werden, dass von den in die Untersuchung einbezogenen Verbindungen die axialen Alkohole durchwegs rascher oxydiert werden als die entsprechenden aquatorialen Epimeren; auf Grund der experimentellen Befunde kann diese Erscheinung entgegen einer in der Literatur vertretenen Hypothese darauf zuruckgefuhrt werden, dass der geschwindigkeitsbestimmende Schritt der Chromsaureoxydation eines gesattigten, sekundaren Alkohols umso rascher ablaft, je grosser der damit verbundene Abbau an nichtklassischer Spannung in der Molekel ist.

J. Schreiber

Papers

Über die relative Geschwindigkeit der Chromosäureoxydation sekundärer, alicyclischer Alkohole. Vorläufige Mitteilung