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1. The use of nitrogen-stabilized carbocations (N-acyliminium ions) as reactive intermediates

This is an important subject in our group regarding our efforts to develop new synthetic pathways. Below are a few examples.

Total synthesis of natural pseudodipeptides

When using allenylmethylsilanes as nucleophiles the products are 1,3-dienes. The coupling of these nucleophiles with glycine cation equivalents is particularly interesting, as it provides novel dienic alpha-amino acid derivatives which are not readily accessible otherwise. Recently, the total synthesis of a natural pseudodipeptide from Philadelphus coronarius (Mock Orange or Boerenjasmijn in Dutch) was completed using this methodology.

Enzymatic resolution of amino acids

In collaboration with DSM, Geleen (L. Duchateau), the enzymatic resolution of amino acids is extensively investigated. This includes the determination of the enantiomeric purity, for with a new chromatography method was developed (M. Berkheij).

Anionic functionalization of the piperazine ring

As an alternative to our cationic chemistry the anionic functionalization of the piperazine ring was investigated in a cooperation with Solvay Pharmaceuticals (Weesp). We showed the possibility of functionalizing N-Boc-piperazine at the 2- and the 6-position via sequential deprotonation/alkylation to give the trans-diallylproduct exclusively. The chemistry of piperazine rings is important because of its occurrence in many pharmaceutical products.