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Author

Gert Kollenz

Other affiliations: University of Queensland
Bio: Gert Kollenz is an academic researcher from University of Graz. The author has contributed to research in topics: Cycloaddition & Nucleophile. The author has an hindex of 23, co-authored 188 publications receiving 1766 citations. Previous affiliations of Gert Kollenz include University of Queensland.


Papers
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Journal ArticleDOI
TL;DR: The most important classes of precursor molecules are 2-diazo-1, 3-diketones, 1,3dioxin-4-ones, 2,3-dihydrofuran-2, 3diones, and beta-ketoacid derivatives as mentioned in this paper.
Abstract: This review describes the methods of generation of alpha-oxoketenes and their use in synthesis. While the ketenes are often generated in situ without direct proof for their existence, methods used for their direct observation are also emphasized. The most important classes of precursor molecules are 2-diazo-1,3-diketones, 1,3-dioxin-4-ones, 2,3-dihydrofuran-2,3-diones, and beta-ketoacid derivatives. Synthetically useful reactions are nucleophilic additions to give carboxylic acid derivatives which can be subjected to further functional group manipulation, [2 + 2] cycloadditions to give four-membered rings, and [2 + 4] cycloaddition chemistry with a wide variety of double-and triple-bonded dienophiles, resulting in numerous six-membered heterocyclic ring systems.

110 citations

Journal ArticleDOI
TL;DR: In this paper, 4-benzoyl-5-phenyl-furan-2,3-dione reacts with various phenylhydrazones at 60-80°C to the pyrazole carboxylic acid, which then can be decarboxylated to 4-bensoyl 1,5-diphenyl-pyrazole (5).
Abstract: 4-Benzoyl-5-phenyl-furan-2,3-dione (1) reacts with various phenylhydrazones2 at 60–80°C to the pyrazole carboxylic acid3 a, which then can be decarboxylated to 4-benzoyl-1,5-diphenyl-pyrazole (5).1 and phenylhydrazine combine again yielding3 a as the main product and the isomeric pyridazinone6 as by-product. At higher temperatures (120–140°C) the reaction of1 with2 a leads to the formation of dibenzoyl acetic acid hydrazide derivatives8.

67 citations

Journal ArticleDOI
TL;DR: The first unambocal example of a direct [2 + 2] cycloaddition reaction of an alpha-oxo ketene was reported in this article, which was later confirmed by X-ray crystallography.
Abstract: Dipivaloylketene (8) is generated by preparative flash vacuum pyrolysis of furandione 6. While dimerization of 8 in apolar and several polar solvents leads to the previously reported [2 + 4] dimer 7, dimerization in the presence of DMSO, tributylphosphine oxide, or pyridine instead surprisingly occurs across the C=O bond of the ketene function, affording dioxinone 9. This is a novel type of alpha-oxo ketene dimerization. The reversibility of both dimerizations and mechanistic pathways for the formation of 9 are discussed. Cycloaddition reactions of 8 with heterocumulenes 10a,b and 12a-c yield [2 + 4] cycloadducts 11a,b and 13a-c, respectively. Oxazinones 13a-c can add a second molecule of 8 to generate novel spiro heterocycles 14a-c. In contrast, oxo ketene 7 reacts with carbodiimides 12a,b, to furnish [2 + 2] adducts 15a,b. This is the first unequivocal example of a direct [2 + 2] cycloaddition reaction of an alpha-oxo ketene. The unexpected formation of these compounds was confirmed by X-ray crystallography (15a). General aspects of [2 + 2] versus [2 + 4] cycloaddition in alpha-oxo ketenes are discussed.

58 citations

Journal ArticleDOI
TL;DR: In this paper, the semicarbazones were combined with loss of water and carbondioxide yielding the 1H-pyrimidine derivatives in moderate yields (30-75%).
Abstract: 4-Benzoyl-5-phenylfuran-2,3-dione (1) and the semicarbazones2, ureas and thioureas6, respectively, combine with loss of water and carbondioxide yielding the 1H-pyrimidine derivatives3 and7, respectively, in moderate yields (30–75%). Hydrolysis of3 b leads to the 1-amino-pyrimidine-2-one4.

52 citations

Journal ArticleDOI
TL;DR: The 1H-pyrazole-3-carboxylic acid or its remarkably stable acid chloride 3 can easily be converted into the corresponding ester or amide derivatives 4 or 5, respectively, from reaction with alcohols or N-nucleophiles.

51 citations


Cited by
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Journal ArticleDOI
TL;DR: This Review highlights recent applications of controlled microwave heating in modern organic synthesis, and discusses some of the underlying phenomena and issues involved.
Abstract: Although fire is now rarely used in synthetic chemistry, it was not until Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied to a reaction vessel in a focused manner. The Bunsen burner was later superseded by the isomantle, oil bath, or hot plate as a source for applying heat to a chemical reaction. In the past few years, heating and driving chemical reactions by microwave energy has been an increasingly popular theme in the scientific community. This nonclassical heating technique is slowly moving from a laboratory curiosity to an established technique that is heavily used in both academia and industry. The efficiency of "microwave flash heating" in dramatically reducing reaction times (from days and hours to minutes and seconds) is just one of the many advantages. This Review highlights recent applications of controlled microwave heating in modern organic synthesis, and discusses some of the underlying phenomena and issues involved.

3,044 citations

Journal ArticleDOI
TL;DR: The current state-of-the-art in graphene oxide reduction, consisting of more than 50 types of reducing agent, will be reviewed from a synthetic chemistry point of view to understand the efficiency of these reducing agents for the reduction of graphene oxide.
Abstract: The chemical reduction of graphene oxide is a promising route towards the large scale production of graphene for commercial applications. The current state-of-the-art in graphene oxide reduction, consisting of more than 50 types of reducing agent, will be reviewed from a synthetic chemistry point of view. Emphasis is placed on the techniques, reaction mechanisms and the quality of the produced graphene. The reducing agents are reviewed under two major categories: (i) those which function according to well-supported mechanisms and (ii) those which function according to proposed mechanisms based on knowledge of organic chemistry. This review will serve as a valuable platform to understand the efficiency of these reducing agents for the reduction of graphene oxide.

1,450 citations

Book
11 Sep 2006
TL;DR: It is shown that domino reactions initiated by oxidation or reduction or reduction, as well as other mechanisms, can be inhibited by various materials, such as Na6(CO3)(SO4), Na2SO4, Na2CO3, and so on.
Abstract: Introduction Cationic domino reactions Anionic domino reactions Radical domino reactions Pericyclic domino reactions Photochemically induced domino processes Transition metal catalysis Domino reactions initiated by oxidation or reduction Enzymes in domino reactions Multicomponent reactions Special techniques in domino reactions

1,337 citations

Journal ArticleDOI
TL;DR: In this paper, a review of synthesis pathways for the preparation of unconventional cellulose derivatives with alternative functional groups and patterns of functionalization is given. But the authors focus on the application of NMR spectroscopy including two-dimensional methods and of chromatographic techniques after specific sample pretreatment as enzymatic and acidic partial or complete depolymerization.

818 citations