Rolf Huisgen

Bio: Rolf Huisgen is an academic researcher from Ludwig Maximilian University of Munich. The author has contributed to research in topics: Cycloaddition & Trifluoromethyl. The author has an hindex of 68, co-authored 679 publications receiving 22161 citations.

1,3-Dipolar Cycloadditions. Past and Future†

Abstract: In contrast to the very large number of special methods applicable to syntheses in the heterocyclic series, relatively few general methods are available. The 1,3-dipolar addition offers a remarkably wide range of utility in the synthesis of five-membered heterocycles. Here the “1,3-dipole”, which can only be represented by zwitterionic octet resonance structures, combines in a cycloaddition with a multiple bond system – the “dipolarophile” – to form an uncharged five-membered ring. Although numerous individual examples of this reaction were known, some even back in the nineteenth century, fruitful development of this synthetic principle has been achieved only in recent years.

1.3‐Dipolare Cycloadditionen Rückschau und Ausblick

Abstract: Einer sehr grosen Zahl spezieller Synthesewege in die heterocyclische in die Reihe steht ein nur bescheidener Satz an Aufbaumethoden von allgemeiner Verwendbarkeit gegenuber. Eine erstaunliche Anwendungsbreite bei der Synthese funfgliedriger Heterocyclen kommt der 1.3-Dipolaren Addition zu. Dabei vereinigt sich der nur mit zwitterionischen Oktett-Grenzformeln wiederzugebende „1.3-Dipol” mit einem Mehrfachbindungssystem, dem „Dipolarophil”, in einer Cycloaddition zum ladungsfreien funfgliedrigen Ring. Wenngleich die Kenntnis zahlreicher Einzelbeispiele bis ins vorige Jahrhundert zuruckreicht, gelangte das Syntheseprinzip erst in den letzten Jahren zu fruchtbarer Entfaltung.

Kinetics and Mechanism of 1,3-Dipolar Cycloadditions

Abstract: Criteria for the mechanism of 1,3-dipolar cycloadditions which lead to 5-membered rings are provided by the stereoselectivity observed with cis-trans isomeric dipolarophiles, by the effect of solvent and substituents on the rate constants, by the activation parameters, and by orientation phenomena. A concerted addition, which can also be described in terms of molecular orbitals and in which the two new σ-bonds are formed simultaneously, although not necessarily at equal rates, offers the best explanation of the experimental facts.

1.3-Dipolare Cycloadditionen, XXXII. Kinetik der Additionen organischer Azide an CC-Mehrfachbindungen

Abstract: Die IR-spektrophotometrisch gemessenen Additionskonstanten des Phenylazids an 27 olefinische und 4 acetylenische Dipolarophile bei 25° liegen im Bereich von 7 Zehnerpotenzen; das Zusammenspiel elektronischer und sterischer Substituenteneffekte beim Dipolarophil wird diskutiert. — Kernsubstituierte Phenylazide befolgen in ihren Additionsgeschwindigkeiten die Hammett-Gleichung, wobei der ρ-Wert vom Dipolarophil abhangt: Maleinsaureanhydrid −1.1, N-Phenyl-maleinimid −0.8, Norbornen +0.88, Cyclopenten +0.9, 1-Pyrrolidino-cyclohexen +2.5. − Die fur vier Azid-Cycloadditionen ermittelten Aktivierungsentropien betragen −26 bis −36 Clausius. Die Additionskonstante des Phenylazids an Pyrrolidino-cyclopenten hangt nur wenig von der Solvenspolaritat ab. All diese Daten weisen auf eine Mehrzentren-Cycloaddition der organischen Azide.

Click Chemistry: Diverse Chemical Function from a Few Good Reactions.

Abstract: Examination of nature's favorite molecules reveals a striking preference for making carbon-heteroatom bonds over carbon-carbon bonds-surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon-heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C-C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C-X-C), an approach we call "click chemistry". Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect "spring-loaded" reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy.

Cu-catalyzed azide-alkyne cycloaddition.

Abstract: The Huisgen 1,3-dipolar cycloaddition reaction of organic azides and alkynes has gained considerable attention in recent years due to the introduction in 2001 of Cu(1) catalysis by Tornoe and Meldal, leading to a major improvement in both rate and regioselectivity of the reaction, as realized independently by the Meldal and the Sharpless laboratories. The great success of the Cu(1) catalyzed reaction is rooted in the fact that it is a virtually quantitative, very robust, insensitive, general, and orthogonal ligation reaction, suitable for even biomolecular ligation and in vivo tagging or as a polymerization reaction for synthesis of long linear polymers. The triazole formed is essentially chemically inert to reactive conditions, e.g. oxidation, reduction, and hydrolysis, and has an intermediate polarity with a dipolar moment of ∼5 D. The basis for the unique properties and rate enhancement for triazole formation under Cu(1) catalysis should be found in the high ∆G of the reaction in combination with the low character of polarity of the dipole of the noncatalyzed thermal reaction, which leads to a considerable activation barrier. In order to understand the reaction in detail, it therefore seems important to spend a moment to consider the structural and mechanistic aspects of the catalysis. The reaction is quite insensitive to reaction conditions as long as Cu(1) is present and may be performed in an aqueous or organic environment both in solution and on solid support.

The Use of Diethyl Azodicarboxylate and Triphenylphosphine in Synthesis and Transformation of Natural Products

Abstract: The reagent formed by combining diethyl azodicarboxylate (DEAD) and triphenylphosphine (TPP) could be utilized in the intermolecular dehydration between an alcohol and various acidic components such as carboxylic acids, phosphoric diesters, imides, and active methylene compounds. By the use of DEAD and TPP, diols and hydroxy acids gave cyclic ethers and lactones, respectively. The reaction of nucleosides with DEAD and TPP afforded triphenylphosphoranylnucleosides. Alcohols reacted with 2,6-di-t-butyl-4-nitrophenol in the presence of DEAD and TPP to give aci-nitroesters which converted into the corresponding carbonyl compounds.