S. Catak

Regioselectivity in the ring opening of non-activated aziridines

S. Stankovic, M. D'Hooghe, S. Catak, M. Waroquier, V. Van Speybroeck, N. De Kimpe, H-J. Ha
Chemical Society Reviews
41, 643-665
2012
A1

Abstract 

In this critical review, the ring opening of non-activated 2-substituted aziridines via intermediate aziridinium salts will be dealt with. Emphasis will be put on the relationship between the observed regioselectivity and inherent structural features such as the nature of the C2 aziridine substituent and the nature of the electrophile and the nucleophile. This overview should allow chemists to gain insight into the factors governing the regioselectivity in aziridinium ring openings (81 references).

Stereoselective synthesis of cis-3,4-disubstituted piperidines through ring transformation of 2-(2-mesyloxyethyl)azetidines

K. Mollet, S. Catak, M. Waroquier, V. Van Speybroeck, M. D'Hooghe, N. De Kimpe
Journal of Organic Chemistry
76 (20), 8364–8375
2011
A1

Abstract 

The reactivity of 2-(2-mesyloxyethyl)azetidines, obtained through monochloroalane reduction and mesylation of the corresponding β-lactams, with regard to different nucleophiles was evaluated for the first time, resulting in the stereoselective preparation of a variety of new 4-acetoxy-, 4-hydroxy-, 4-bromo-, and 4-formyloxypiperidines. During these reactions, transient 1-azoniabicyclo[2.2.0]hexanes were prone to undergo an SN2-type ring opening to afford the final azaheterocycles, which was rationalized by means of a detailed computational analysis. This approach constitutes a convenient alternative for the known preparation of 3,4-disubstituted 5,5-dimethylpiperidines, providing an easy access to the 5,5-nor-dimethyl analogues as valuable templates in medicinal chemistry. Furthermore, cis-4-bromo-3-(phenoxy or benzyloxy)piperidines were elaborated into the piperidin-3-one framework via dehydrobromination followed by acid hydrolysis.

Reactivity of Activated versus Nonactivated 2-(Bromomethyl)aziridines with respect to Sodium Methoxide: a Combined Computational and Experimental Study

H. Goossens, K. Vervisch, S. Catak, S. Stankovic, M. D'Hooghe, F. De Proft, P. Geerlings, N. De Kimpe, M. Waroquier, V. Van Speybroeck
Journal of Organic Chemistry
76 (21), 8698-8709
2011
A1

Abstract 

The difference in reactivity between the activated 2-bromomethyl-1-tosylaziridine and the non-activated 1-benzyl-2-(bromomethyl)aziridine with respect to sodium methoxide was analyzed by means of DFT calculations within the supermolecule approach, taking into account explicit solvent molecules. In addition, the reactivity of epibromohydrin with regard to sodium methoxide was assessed as well. The barriers for direct displacement of bromide by methoxide in methanol are comparable for all three heterocyclic species under study. However, ring opening was found to be only feasible for the epoxide and the activated aziridine, and not for the non-activated aziridine. According to these computational analyses, the synthesis of chiral 2-substituted 1-tosylaziridines can take place with inversion (through ring opening/ring closure) or retention (through direct bromide displacement) of configuration upon treatment of the corresponding 2-(bromomethyl)aziridines with one equivalent of a nucleophile, whereas chiral 2-substituted 1-benzylaziridines are selectively obtained with retention of configuration (via direct bromide displacement). Furthermore, the computational results showed that explicit accounting for solvent molecules is required to describe the free energy profile correctly. To verify the computational findings experimentally, chiral 1-benzyl-2-(bromomethyl)aziridines and 2-bromomethyl-1-tosylaziridines were treated with sodium methoxide in methanol. The presented work concerning the reactivity of 2-bromomethyl-1-tosylaziridine stands in contrast to the behaviour of the corresponding 1-tosyl-2-(tosyloxymethyl)aziridine with respect to nucleophiles, which undergoes a clean ring-opening/ring-closure process with inversion of configuration at the asymmetric aziridine carbon atom.

Furan-Oxidation-Triggered Inducible DNA Cross-Linking: Acyclic Versus Cyclic Furan-Containing Building Blocks—On the Benefit of Restoring the Cyclic Sugar Backbone

K. Stevens, D.D. Claeys, S. Catak, S. Figaroli, M. Hocek, J.M. Tromp, S. Schürch, V. Van Speybroeck, A. Madder
Chemistry - A European Journal
17 (25), 6940-6953
2011
A1

Abstract 

Oligodeoxynucleotides incorporating a reactive functionality can cause irreversible cross-linking to the target sequence and have been widely studied for their potential in inhibition of gene expression or development of diagnostic probes for gene analysis. Reactive oligonucleotides further show potential in a supramolecular context for the construction of nanometer-sized DNA-based objects. Inspired by the cytochrome P450 catalyzed transformation of furan into a reactive enal species, we recently introduced a furan-oxidation-based methodology for cross-linking of nucleic acids. Previous experiments using a simple acyclic building block equipped with a furan moiety for incorporation into oligodeoxynucleotides have shown that cross-linking occurs in a very fast and efficient way and that substantial amounts of stable, site-selectively cross-linked species can be isolated. Given the destabilization of duplexes observed upon introduction of the initially designed furan-modified building block into DNA duplexes, we explore here the potential benefits of two new building blocks featuring an extended aromatic system and a restored cyclic backbone. Thorough experimental analysis of cross-linking reactions in a series of contexts, combined with theoretical calculations, permit structural characterization of the formed species and allow assessment of the origin of the enhanced cross-link selectivity. Our experiments clearly show that the modular nature of the furan-modified building blocks used in the current cross-linking strategy allow for fine tuning of both yield and selectivity of the interstrand cross-linking reaction.

Synthesis of 2-hydroxy-1,4-oxazin-3-ones through ring transformation of 3-hydroxy-4-(1,2-dihydroxyethyl)-β-lactams and study of their reactivity

ISBN/ISSN:
Talk

Conference / event / venue 

12th Chemistry Conference for Young Scientists
Blankenberge, Belgium
Thursday, 27 February, 2014 to Friday, 28 February, 2014

Synthesis of 2-hydroxy-1,4-oxazin-3-ones through ring transformation of 3-hydroxy-4-(1,2-dihydroxyethyl)-β-lactams and study of their reactivity

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Talk

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17th Sigma-Aldrich Organic Synthesis Meeting
Blankenberge, Belgium
Thursday, 5 December, 2013 to Friday, 6 December, 2013

Cationic ring-opening polymerization of 2-propyl-2-oxazolines: understanding structural effects on polymerization behavior based on molecular modeling

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Talk

Conference / event / venue 

248th National Meeting of the American-Chemical-Society (ACS 2014 )
San Francisco, CA
Sunday, 10 August, 2014 to Thursday, 14 August, 2014

Computational insight into the polymerization of conjugated electroluminescent polymer PPV: Diradical character of monomers and dimers

ISBN/ISSN:0065-7727
Talk

Conference / event / venue 

250th ACS National Meeting & Exposition - Division of Catalysis Science and Technology (CATL)
Boston, MA, USA
Sunday, 16 August, 2015 to Thursday, 20 August, 2015

Towards an understanding of the role of π-cation interactions in accelerating living cationic ring-opening polymerization of unsaturated alkyl-2-oxazolines

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Poster

Conference / event / venue 

Cecam Workshop - Frontiers and challenges of computing metals for biochemical, medical and technological applications
Paris, France
Wednesday, 11 July, 2018 to Friday, 13 July, 2018

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