Ruthenium-catalyzed allylic alkylations of chelated enolates using vinyl dioxolanon-2-ones.

4-Vinyl-substituted 1,3-dioxolan-2-ones are found to be good substrates for Ru-catalyzed allylic alkylations of chelated amino acid ester enolates. cis-1,3-Dioxolan-2-ones are more reactive than the corresponding trans-isomers. The attack occurs preferentially with regioretention at the position of the leaving group with perfect chirality transfer.

Selective peptide modifications via ruthenium-catalyzed allylic alkylations.

Ruthenium-catalyzed allylic alkylations are an interesting alternative to palladium-catalyzed processes, since they can provide products which are not accessible under Pd-catalysis. Chiral terminal allylic substrates can be reacted with perfect stereo- and regioretention, and also (Z)-configured allylic substrates can be converted isomerization-free. This allows highly stereoselective modifications of peptides at glycine subunits.

[(p-Cymene)RuCl2 ]2 : an efficient catalyst for highly regioselective allylic alkylations of chelated amino acid ester enolates.

Chelated amino acid ester enolates are excellent nucleophiles for ruthenium-catalyzed allylic alkylations. Although [Cp*Ru(MeCN)3 ]PF6 was found to be the most reactive catalyst investigated, with the resulting allyl complexes reacting at temperatures as low as -78 °C, unfortunately the process took place with only moderate regio- and diastereoselectivity. In contrast, [(p-cymene)RuCl2 ]2 allowed allylations to be performed with a high degree of regioretention.

Highly stereoselective modifications of peptides via Pd-catalyzed allylic alkylation of internal peptide amide enolates.

Pd-catalyzed allylations are excellent tools for stereoselective peptide modifications, showing several advantages compared to normal alkylations. Reactions of internal peptide amide enolates with Pd-allyl complexes proceed not only with high yields of up to 86%, they show also high regio- and diastereoselectivities (88-99%), giving rise to the trans-configured products. Therefore, this protocol is a powerful synthetic tool for the synthesis of natural product and drug molecules.

Highly regioselective ruthenium-catalyzed allylic alkylations of chelated enolates.

Ru-catalyzed allylic alkylations are a highly interesting alternative to Pd-catalyzed reactions. Ru complexes show a high tendency for regioretention, especially for branched and (Z)-configured substrates, and they do not undergo isomerization of the allyl intermediates formed. Therefore, (Z)-substrates conserve their olefin geometry, and a perfect chirality transfer is observed with optically active substrates.