1,3 -Dipolar Cycloadditions: Click Chemistry for a New Synthesis of 5-Substituted Tetrazoles and Applications in Organocatalysis Thèse présentée à la Faculté des Sciences Institut de Chimie Université de Neuchâtel Pour l’obtention du grade de Docteur ès Sciences Par Valentina Aureggi Chimiste diplômée de l’Université de l’ Insubria (Italie) Acceptée sur proposition du jury: Prof. Reinhard Neier, directeur de thèse Prof. Gottfried Sedelmeier (Novartis Pharma AG, Bâle), directeur de thèse Prof. Thomas Ward, rapporteur Prof. Dieter Seebach (ETH, Zőrich), rapporteur Soutenue le 3 Juillet 2007 Université de Neuchâtel 2007 Acknowledgments This work was supported by Novartis Pharma AG (Basel, Switzerland, Process Research Development). First and foremost, I would like to thank my supervisor Prof. Gottfried Sedelmeier for giving me the chance to conduct my Ph.D. work with him. He has always generously supported me and his wise guidance and his strong passion for science helped me to grow personally and professionally. Through out my stay, his belief and trust in my abilities allowed me to grow as a chemist and strengthen my confidence. The project we developed together for the synthesis of tetrazole rings is a strong contribution to the scientific community and I really believe that it will find in the future a wide industrial application. It was a pleasure working every day with him and his team, the shared successes and difficulties which are always part of research, and I am really proud to have given my personal contribution to the project. I also would like to express a special thanks to Dr. Gerhard Penn for supporting me in a administrative and scientific way and allow me to make my thesis in PR&D department. In addition, I would like to thank him for his expert opinion concerning my work, his patience, and constructive advise. I would like to thank Dr. Reto Fischer to allow me to complete my Ph.D. thesis in the PR&D Department and supporting me in the publications of our scientific work. I would like to address my special thanks to Prof. Reinhad Neier (University of Neuchatel) since the time I spent in Neuchatel for my Erasmus exchange, he always supported me with important advices, interesting discussions, and he encouraged me after my university work to continue conducting research by making a Ph.D thesis. I want to thank him also for his highly efficient academic assistance and his valuable interest in my thesis. I am grateful to all people in PR&D department at Novartis for the time they dedicated to me for technical and scientific advice. Special thanks to Brigitte Berod and Dominique Grimler for the technical support. It was a pleasure for me to appreciate their experience and for the time they spent to teach me techniques. In addition I would like to thank Adnan Osmani, Alain Litzler and Joelle Fruh for technical, administrative support and friendship. I would like to thank all the people who allowed me to perform specific experiments: Dr. Christian Mathes, Dr. Walter Prikoszovich and Bernard Linder for the FT-IR study concerning the azides formation; Dr. Bernhard Erb and Friedrich Schuerch for the preparation in kilo-lab of 1.5 Kg of ( R)-2 (1 H-tetrazol-5-yl)-pyrrolidine-1-carboxylic acid benzyl ester 113 and confirm the high reproducibility of our new methodology; Paul Schultheiss (NIBR) for the hydrogenation step of 112 and 113 ; Dr. Kamal Azzaoui (MLI) for the modelling study of ortho -alogen-phenyltetrazoles formation; Dr. Jacques Wiss, Dr. Christoph Heuberger and Raphael Ruckstuhl for differential scanning calorimetry data; Dr. Beatrix Wagner and her co-worker Hansrudolf Walter for all the X-ray structure determinations and for the important discussion and proof reading of the Chapter 4 of my thesis. I am grateful to all people from the Analytical Department for their valuable scientific investigations. Special thanks to Serge Moss for spending time to teach me the importance of the informations from the IR spectroscopy; Monique Ponelle, Emine Sager, Quitterie Michon and Dr. Harald Schroeder for NMR analyses; Elodie Letot for IR and UV-analysis and Francis Roll for MS-spectroscopy. Without their aid, this thesis would never have attained the present form. I would like to thank Dr. Stuart J. Mickel, Dr. Walter Prikoszovich, Dr. Rudolf Giger, Dr. Christoph Krell and Dr. Thierry Schlama for all the scientific and personal advices during my stay in PR&D. Also within Novartis, I did not only find professional support but also found real friendship that I will look forward to continue in the future. A special thanks to all those people who were more than colleagues and who were part of my life during my time in Basel and who made my Ph.D. time unforgettable: Aurélien Bigot, Dr. Jarred T. Blank, Dr. Thomas Ruch and Cornelia Gasser, Dr. Benjamin Martin, Dr. Kamal Azzaoui, Dr. Nabila Sekkat, Dr. Carole Pissot, Dr. Cedric Berger, Quitterie Michon, Veronica Denti, Dr. Francesca Frigerio, Dr. Deborah Gonzalez Mantero, Alessandro Marchesini, Dr. Marcella Ramelli, Valeria Botomei, and of course a special thanks to Aurélien who encouraged and emotional supported me every day during the last four years. A special thanks to all the friends of the Young Swiss Chemical Society who gave me the opportunity to be the treasurer during the last three years. A special thanks to my family for dedication and supporting me during my education. Un ringraziamento speciale alla mia famiglia, specialmente a mio padre e mia madre per avermi insegnato i veri valori nella vita e avermi sostenuto economicamente e moralmente nel corso degli anni. Un ringraziamento speciale a mio padre per avermi trasmesso la curiosità e la passione per la scienza come filosofia di vita ed è loro a cui voglio dedicare questo mio lavoro con la promessa che cercherò sempre di mantenere il mio entusiasmo. Abbreviations Symbol Entity Abs. Absorbance Ac Acetyl AcOH Acetic acid Al. Aliphatic Ar. Aromatic Bn Benzyl Boc tert -Butoxycarbonyl BOM 1-Benzyloxymethyl br Broad signal BuOH Butanol tBu tert -Butyl calc. Calculated Cbz Benzyloxycarbonyl Cq Quaternary carbon 1D, 2D, 3D One-, two-, three-dimensional d Doublet (NMR) DBU 1,8-Diazabicyclo[5.4.0]undec-7-ene DMF Dimethylformammide DMSO Dimethylsulfoxyde dr Diastomeric ratio ee Enantiomeric excess EtOAc Ethyl acetate FT-IR Fourier Transform Infrared (Spectroscopy) HPLC High Performance Liquid Chromatography HR-MS High Resolution Mass Spectroscopy IR Infrared (Spectroscopy) J Coupling constant m Multiplet (NMR) Medium (IR) MA Mass of the acid (MS) MB Mass of the base (MS) mp Melting point MS Mass Spectroscopy NMR Nuclear Magnetic Resonance Pd/C Palladium on charcoal Ph Phenyl PMB p-Methoxy benzyl PTC Phase Transfer Catalysis q Quartet (NMR) Rf Retention factor r.t. Room temperature s Singlet (NMR) Strong (IR) sep Septet (NMR) t Triplet (NMR) TBAF Tetrabuthylammonium fluoride TBDMS tButyl dimethyl silyl TFA Trifluoroacetic acid THF Tetrahydrofurane TLC Thin Layer Chromatography TMS Trimethylsilane Tr Trityl Ts Tosyl TS Transition State UV Ultraviolet Spectroscopy vibr. Vibration (IR) w Weak (IR) Entity Symbol Unit 3 Calculated density in g/cm Dc Final structure agreement factors R1, wR2 Length Å Angstrom Molecular Weigh MW g/mol Number of molecules per unit cell Z Optical rotation 25 ° [α ]D Pressure bar Bar Temperature T ° C Time t min h Unit-cell angles α, β, γ ° Unit-cell lengths a, b, c Å Volume L Liter 3 Unit-cell volume V Å -1 Vibration frequency ν~ cm λ nm Wave number cm -1 Wave number Keywords Tetrazole, Sartans, Nitriles, Dialkylaluminum azide, Cycloaddition, Alkylation, Methylation, Organocatalysis, Enamine Summary Tetrazoles are a class of heterocycles with a wide range of applications in medicinal chemistry and in material sciences 1. However a versatile method to synthesize tetrazoles through safe protocols is still highly desirable. Indeed each of the general known procedures uses either toxic metals, expensive reagents, harsh reaction conditions and may lead to the formation of dangerous hydrazoic acid or explosive sublimates. We report herein the discovery and development of a novel efficient process for transforming a wide variety of nitriles into the corresponding tetrazoles in high yield, using a simple and safe protocol. It has been found that the organoaluminum azides are effective reagents for the direct conversion of nitriles to tetrazoles (Scheme 1) 141,142 . Toluene R2AlCl + NaN3 R2AlN3 + NaCl 0°C to r.t. 4-6h N R2AlN3 NH R' C N R' Toluene N N -40 to 120°C Scheme 1. Novel synthesis of tetrazole rings The organic soluble dialkylaluminum azides are prepared in a short time (4-6 h, r.t.) from the corresponding cheap dialkylaluminum chlorides. The cycloaddition occurs under mild conditions, and it is possible to synthesize a broad range of tetrazole derivatives with a high selectivity. This methodology can be applied to the synthesis of the pyrrolidine tetrazole, a versatile alternative of proline in organocatalysis. A variety of new catalysts based on pyrrolidine tetrazole skeleton are therefore efficiently prepared and tested 142 . Resumé Les besoins récents en chimie organique de synthèse appliquée focalisent les efforts des chercheurs au développement de nouvelles voies efficaces et versatiles pour la préparation de molécules bioactives, en prenant en comptes en particulier les critères économiques et environnementaux. Nous avons développé une méthode novatrice et écologique pour la préparation de tetrazoles 141,142 . Ce groupe fonctionnel trouve des applications dans des domaines variés allant des matériaux aux explosifs, et est d’un intérêt tout particulier en chimie médicinale 1 . Cette importance a conduit au développement de diverses méthodes de préparation des tétrazoles, toutes présentant cependant des désavantages majeurs comme l’utilisation de réactifs toxiques ou explosifs, entre autres. La méthode alternative que nous avons développée permet la formation de tétrazoles à partir de nitriles en utilisant des azides de dialkylaluminium, qui possèdent l’avantage d’être des réactifs bon marché et non toxiques et permettent la préparation d’une large variété de tétrazoles de façon très efficace, adaptable à l’échelle industrielle (Scheme 1).