In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

Palladium-catalyzed cross-coupling reactions in total synthesis.

Wenn man die Entwicklung der organischen Chemie betrachtet, kommt man schnell zu dem Schluss, dass kein Reaktionstyp dieses Gebiet in vergleichbarer Weise gepragt hat wie die Kohlenstoff-Kohlenstoff-Kupplungen. Grignard-, Diels-Alder- und Wittig-Reaktionen sind nur drei herausragende Beispiele fur solche Prozesse, die im vergangenen Jahrhundert zweifellos entscheidend am Aufstieg der chemischen Synthese beteiligt waren. Im letzten Viertel des 20. Jahrhunderts bereicherte eine neue Familie von leistungsfahigen Reaktionen zur Knupfung von Kohlenstoff-Kohlenstoff-Bindungen das Repertoire der Synthesechemie: die ubergangsmetallkatalysierten Reaktionen, allen voran die palladiumkatalysierten Kreuzkupplungen. In diesem Aufsatz werden Auszuge aus einer Reihe von ausgewahlten Synthesen diskutiert. Die Beispiele sollen die enorme Leistungsfahigkeit dieser Prozesse in der Kunst der Totalsynthese aufzeigen und ihr Potenzial fur zukunftige chemische Synthesen unterstreichen.

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Palladiumkatalysierte Kreuzkupplungen in der Totalsynthese

Macrolactonizations in the Total Synthesis of Natural Products

Scandium trifluoromethanesulfonate (triflate), which is commercially available, is a practical and useful Lewis acid catalyst for acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of p-nitrobenzoic anhydrides. The remarkably high catalytic activity of scandium triflate can be used for assisting the acylation by acid anhydrides of not only primary alcohols but also sterically-hindered secondary or tertiary alcohols. The method presented is especially effective for selective macrolactonization of ω-hydroxy carboxylic acids.

Scandium Trifluoromethanesulfonate as an Extremely Active Lewis Acid Catalyst in Acylation of Alcohols with Acid Anhydrides and Mixed Anhydrides.

Various carboxylic esters are obtained at room temperature in excellent yields with high chemoselectivities from nearly equimolar amounts of carboxylic acids and alcohols using 2-methyl-6-nitrobenzoic anhydride with triethylamine by the promotion of a basic catalyst such as 4-(dimethylamino)pyridine. A variety of lactones are also prepared in high yields at room temperature from the corresponding ω-hydroxycarboxylic acids with use of 2-methyl-6-nitrobenzoic anhydride in the presence of 4-(dimethylamino)pyridine. A similar reaction occurs with triethylamine when using a catalytic amount of 4-(dimethylamino)pyridine 1-oxide as an effective promoter for the intramolecular condensation reaction. These methods are successfully applied to the synthesis of erythro-aleuritic acid lactone and an eight-membered-ring lactone moiety of octalactins A and B. The efficiency of the cyclizations is compared to those of other reported lactonizations.

An effective use of benzoic anhydride and its derivatives for the synthesis of carboxylic esters and lactones: A powerful and convenient mixed anhydride method promoted by basic catalysts

A rapid and mild esterification method using carboxylic 2,4,6-trichlorobenzoic anhydrides in the presence of 4-dimethylaminopyridine was developed. The method was also successfully applied to the synthesis of large-ring lactones, including DL-2,4,6-tridemethyl-3-deoxymethynolide.

Kuniko Hirata

Papers

A rapid esterification by means of mixed anhydride and its application to large-ring lactonization.