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Chiral thiophene-salen chromium complexes were investigated in their monomeric form as soluble catalysts in the enantioselective Henry reaction of several aldehydes. The anodic polymerization of one complex led to an insoluble powder that was successfully used as a heterogeneous catalyst for the transformation of 2-methoxybenzaldehyde with enantiomeric excesses up to 77%. The polymerized catalyst was recovered and also recycled in an original multisubstrate procedure.

New chiral thiophene-salen ligands have been synthesized and the corresponding chromium complexes proved to be efficient catalysts for promoting asymmetric hetero-DielsAlder reactions with good activities and high enantioselectivities (up to 88 % ee). These complexes were successfully electropolymerized to give chiral polymers as insoluble powders for use in asymmetric heterogeneous catalysis. When engaged in successive hetero-Diels-Alder reactions,

Chiral salen-type complexes have already been proven to be particularly useful asymmetric catalysts for the preparation of a wide range of enantioenriched products. Research for efficient recovery and recycling of such complexes is ongoing and has already demonstrated the value of these procedures in terms of atom economy and overall economical savings. Results reported in the near past (2006-2009) dealing with the use of recyclable chiral salen complexes are summarized here, classified according to the type of heterogenization procedures involved.

A general strategy for the amino acid homologation via Blaise reaction and subsequent reduction is presented. This strategy involves the preparation of protected alpha-amino nitriles from the corresponding amino acids, followed by the zinc-mediated condensation of tert-butyl bromoacetate, to give the imidazolidones after iminozincate cyclization. Reduction gave the saturated imidazolidinones with cis or trans stereochemistry, depending on the reduction conditions. This strategy was applied to nonfunctionalized amino acids and to functionalized amino acids such as serine and aspartic acid. Additionally, acidic hydrolysis of cis or trans imidazolidinones to the corresponding chiral 4-aminopyrrolidones is described.

International audienceThe synthesis of acrylate derivatives bearing a difluorophosphonic acid function has been realized by ring-opening reaction of oxacycles and alkylation of fluorinated carbanions. Their use in self-etch adhesives is reported. The resulting adhesives based on difluorophosphonic acid monomers provide significantly higher dentin shear bond strength (SBS) than the one based on phosphonic acid, mainly due to the presence of fluorine atoms

An electrogenerated heterogeneous chiral (poly)salen-thiophene chromium complex successfully promoted different asymmetric catalytic reactions in an original successive manner, demonstrating its high stability and versatility.

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