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Dive into the research topics where Tor E. Kristensen is active.

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Featured researches published by Tor E. Kristensen.


Journal of Organic Chemistry | 2010

A General Approach for Preparation of Polymer-Supported Chiral Organocatalysts via Acrylic Copolymerization

Tor E. Kristensen; Kristian Vestli; Martin Gjerde Jakobsen; Finn Knut Hansen; Tore Hansen

Polymer-supported chiral organocatalysts, as well as most other forms of immobilized catalysts, are traditionally prepared by a postmodification approach where modified catalyst precursors are anchored onto prefabricated polymer beads. Herein, we report an alternative and more scalable approach where polymer-supported chiral enamine and iminium organocatalysts are prepared in a bottom-up fashion where methacrylic functional monomers are prepared in an entirely nonchromatographic manner and subsequently copolymerized with suitable comonomers to give cross-linked polymer beads. All syntheses have been conducted on multigram scale for all intermediates and finished polymer products, and the catalysts have proven successful in reactions taking place in solvents spanning a wide range of solvent polarity. While polymer-supported proline and prolineamides generally demonstrated excellent results and recycling robustness in asymmetric aldol reactions of ketones and benzaldehydes, the simplest type of Jørgensen/Hayashi diarylprolinol TMS-ether showed excellent selectivity, but rather sluggish reactivity in the Enders-type asymmetric cascade. The polymer-supported version of the first-generation MacMillan imidazolidinone had a pattern of reactivity very similar to that of the monomeric catalyst, but is too unstable to allow recycling.


Organic Letters | 2009

Synthesis of Acrylic Polymer Beads for Solid-Supported Proline-Derived Organocatalysts

Tor E. Kristensen; Kristian Vestli; Kim A. Fredriksen; Finn Knut Hansen; Tore Hansen

A completely non-chromatographic and highly large-scale adaptable synthesis of acrylic polymer beads containing proline and prolineamides has been developed. Novel monomeric proline (meth)acrylates are prepared from hydroxyproline in only one step. Free-radical copolymerization then gives solid-supported proline organocatalysts directly in as little as two steps overall, without using any prefabricated solid supports, by using either droplet or dispersion polymerization. These affordable acrylic beads have highly favorable and adjustable swelling characteristics and are excellent reusable catalysts for organocatalytic reactions.


Beilstein Journal of Organic Chemistry | 2012

Combined bead polymerization and Cinchona organocatalyst immobilization by thiol-ene addition.

Kim A. Fredriksen; Tor E. Kristensen; Tore Hansen

Summary In this work, we report an unusually concise immobilization of Cinchona organocatalysts using thiol–ene chemistry, in which catalyst immobilization and bead polymerization is combined in a single step. A solution of azo initiator, polyfunctional thiol, polyfunctional alkene and an unmodified Cinchona-derived organocatalyst in a solvent is suspended in water and copolymerized on heating by thiol–ene additions. The resultant spherical and gel-type polymer beads have been evaluated as organocatalysts in catalytic asymmetric transformations.


Beilstein Journal of Organic Chemistry | 2015

Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications

Tor E. Kristensen

Summary Amino acids, whether natural, semisynthetic or synthetic, are among the most important and useful chiral building blocks available for organic chemical synthesis. In principle, they can function as inexpensive, chiral and densely functionalized starting materials. On the other hand, the use of amino acid starting materials routinely necessitates protective group chemistry, and in reality, large-scale preparations of even the simplest side-chain derivatives of many amino acids often become annoyingly strenuous due to the necessity of employing protecting groups, on one or more of the amino acid functionalities, during the synthetic sequence. However, in the case of hydroxyamino acids such as hydroxyproline, serine, threonine, tyrosine and 3,4-dihydroxyphenylalanine (DOPA), many O-acyl side-chain derivatives are directly accessible via a particularly expedient and scalable method not commonly applied until recently. Direct acylation of unprotected hydroxyamino acids with acyl halides or carboxylic anhydrides under appropriately acidic reaction conditions renders possible chemoselective O-acylation, furnishing the corresponding side-chain esters directly, on multigram-scale, in a single step, and without chromatographic purification. Assuming a certain degree of stability under acidic reaction conditions, the method is also applicable for a number of related compounds, such as various amino alcohols and the thiol-functional amino acid cysteine. While the basic methodology underlying this approach has been known for decades, it has evolved through recent developments connected to amino acid-derived chiral organocatalysts to become a more widely recognized procedure for large-scale preparation of many useful side-chain derivatives of hydroxyamino acids and related compounds. Such derivatives are useful in peptide chemistry and drug development, as amino acid amphiphiles for asymmetric catalysis, and as amino acid acrylic precursors for preparation of catalytically active macromolecular networks in the form of soluble polymers, crosslinked polymer beads or nanoparticulate systems. The objective of the present review is to increase awareness of the existence and convenience of this methodology, assess its competitiveness compared to newer and more elaborate procedures for chemoselective O-acylation reactions, spur its further development, and finally to chronicle the informative, but poorly documented history of its development.


European Journal of Organic Chemistry | 2010

Polymer-Supported Chiral Organocatalysts: Synthetic Strategies for the Road Towards Affordable Polymeric Immobilization

Tor E. Kristensen; Tore Hansen


European Journal of Organic Chemistry | 2009

New Phenylglycine-Derived Primary Amine Organocatalysts for the Preparation of Optically Active Warfarin

Tor E. Kristensen; Kristian Vestli; Finn Knut Hansen; Tore Hansen


European Journal of Organic Chemistry | 2009

The Selective O-Acylation of Hydroxyproline as a Convenient Method for the Large-Scale Preparation of Novel Proline Polymers and Amphiphiles

Tor E. Kristensen; Finn Knut Hansen; Tore Hansen


Tetrahedron-asymmetry | 2011

Enantioselectivity, swelling and stability of 4-hydroxyprolinol containing acrylic polymer beads in the asymmetric reduction of ketones

Thor Håkon Krane Thvedt; Tor E. Kristensen; Eirik Sundby; Tore Hansen; Bård Helge Hoff


Propellants, Explosives, Pyrotechnics | 2012

Neutral Polymeric Bonding Agents (NPBA) and Their Use in Smokeless Composite Rocket Propellants Based on HMX‐GAP‐BuNENA

Eva Landsem; Tomas Lunde Jensen; Finn Knut Hansen; Erik Unneberg; Tor E. Kristensen


Propellants, Explosives, Pyrotechnics | 2013

Isocyanate-Free and Dual Curing of Smokeless Composite Rocket Propellants

Eva Landsem; Tomas Lunde Jensen; Tor E. Kristensen; Finn Knut Hansen; Tore Benneche; Erik Unneberg

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Erik Unneberg

Norwegian Defence Research Establishment

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Tomas Lunde Jensen

Norwegian Defence Research Establishment

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Eva Landsem

Norwegian Defence Research Establishment

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Bård Helge Hoff

Norwegian University of Science and Technology

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Thor Håkon Krane Thvedt

Norwegian University of Science and Technology

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