Mathematisch-Naturwissenschaftliche Fakultät

Institut für Chemie

Fachgebiet: Organokatalyse

Betreuer: Dr. Thomas Werner

M. Sc. Marcel Hoffmann
(e-mail: )

Development of catalytic Wittig Reactions

The Wittig reaction is one of the most common and reliable methods for the regioselective and stereoselective carbonyl olefination in scientific synthesis as well as in industrial practice for the preparation of natural and pharmaceutical compounds. Phosphines are used as stoichiometric reagents in the reaction which are ultimately converted into phosphine oxides. These are usually regarded as waste products. By the application of silanes as chemoselective reducing agents phosphines can be regenerated leading to a catalytic Wittig reaction. The commercially available tributylphosphine oxide was used as a precatalyst for the olefination of several aromatic, heteroaromatic and aliphatic aldehydes with organo halides in combination with phenylsilane as reducing agent. The corresponding alkenes were obtained in moderate to good yields and high E/Z-selectivities. These yields could be increased by the employment of a cyclic tunable phosphine oxide which is easier to reduce than the acyclic counter parts and trimethoxy silane as the reducing agent. Also ketones were suitable substrates in this reaction.

An asymmetric catalytic Wittig reaction was investigated by the reaction of a meso carbonyl compound and chiral phosphines. As a model reaction the intramolecular conversion of a meso triketone leading to the bis-nor-Wieland-Miescher ketone was selected. The commercially available Me-BPE was identified as a suitable catalyst for the Wittig reaction yielding the bis-nor-Wieland-Miescher ketone in 53% yield and 36% enantiomeric excess. This result represents the first example of an asymmetric catalytic Wittig reaction to the best of our knowledge.