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IDPi Catalysis: The Hosomi-Sakurai Allylation and a Mukaiyama Aldol Reaction with Enolsilanes of Acetaldehyde

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Schreyer,  Lucas
Research Department List, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Schreyer, L. (2018). IDPi Catalysis: The Hosomi-Sakurai Allylation and a Mukaiyama Aldol Reaction with Enolsilanes of Acetaldehyde. PhD Thesis, Universität zu Köln, Köln.


Cite as: http://hdl.handle.net/21.11116/0000-0003-5761-E
Abstract
The following work describes the development and application of imidodiphosphorimidates (IDPi) in enantioselective organic Lewis acid catalysis. This new class of catalysts was generated by the replacement of the O-atoms of the Brønsted acidic and Lewis basic sites of the core of previously developed imidodophosphate (IDP) catalysts by NTf groups (the "Yagupolskii principle"). IDPi are of sufficiently enhanced Brønsted acidity and weakened Lewis basicity for the application in "silylium" Lewis acid catalysed transformations. Therefore, while IDP were catalytically inactive, silylated IDPi activated aldehydes for the addition of even weakly nucleophilic silanes. One long standing problem in this regard has been the enantioselective addition of allyltrimethylsilane to aldehydes, the "Hosomi-Sakurai" allylation. This transformation was beyond reach with the previously developed organic Lewis acid disulfonimide (DSI) precatalysts. By fine-tuning of the catalyst structure, a highly enantioselective allylation of a variety of aromatic and even simple aliphatic aldehydes was enabled, at catalysts loadings as low as 0.05mol%. The products obtained by this method, homoallylic alcohols, are frequently applied as intermediates for the synthesis of (protected) acetaldehyde aldols within 2 more steps, by O-protection and olefin oxidation. With our powerful new catalysts, we realized a single step enantioselective method to synthesize these aldols in a Mukaiyama aldol reaction with simple enolsilanes of acetaldehyde. Various functionalized and unfunctionalized aromatic and aliphatic aldehydes were readily transformed into the corresponding single aldolisation products in high yields and enantiomeric ratios, at short reaction times (5 min to 10 h) with low catalyst loadings (0.5-2.0 mol%). The method described in this thesis have solved long-standing problems in organic synthesis. Inexpensive, non-toxic allyltrimethylsilane can now be used for highly enantioselective allylations of aldehydes. While other strong Lewis acids such as triflimide catalyse the oligomerisation of enolsilanes of acetaldehyde, our IDPi successfully distinguishes substrate and product aldehydes, enabling highly enantioselective single step syntheses of aldols which previously were accessible in only sequences of several transformations.