Asymmetric organocatalysis has experienced an incredible development since the beginning of this century. The expansion of the field has led to a large number of efficient types of catalysts. One group, the diarylprolinol silyl ethers, was introduced in 2005 and has been established as one of the most frequently used in aminocatalysis. In this Minireview, we will take a look in the rear-view mirror, ten years after the introduction of the diarylprolinol silyl ethers. We will focus on the perspectives of the different activation modes made available by this catalytic system. Starting with a short introduction to aminocatalysis, we will outline the properties that have made the diarylprolinol silyl ethers a common choice of catalyst. Furthermore, we will describe the major tendencies in the activation and reaction concepts developed with regard to reactivity patterns and combinations with other activation concepts.

The first asymmetric regio- and diastereodivergent γ-allylation of cyclic α,β-unsaturated aldehydes based on combined organocatalysis and transition-metal catalysis is disclosed. By combining an aminocatalyst with an iridium catalyst, both diastereomers of branched allylated products can be achieved in moderate to good yields and excellent regio- and stereoselectivities. Furthermore, by replacing the iridium catalyst with a palladium catalyst, the linear allylated products are formed in good yields and excellent regio- and enantioselectivities. The developed method thus provides selective access to all six isomers of the γ-allylated product in a divergent fashion by choosing the appropriate combination of organocatalyst, transition-metal catalyst, and ligand.

Cross-conjugated trienamines are introduced as a new concept in asymmetric organocatalysis. These intermediates are applied in highly enantioselective Diels–Alder and addition reactions, providing functionalized bicyclo[2.2.2]octane compounds and γ′-addition products, respectively. The nature of the transformations and the intermediates involved are investigated by computational calculations and NMR analysis.

Azolopyrimidines are efficiently prepared by direct imidoyl C-H bond activation. Annulations of N-azolo imines with sulfoxonium ylides and diazoketones under redox-neutral conditions and alkynes under oxidizing conditions provide products with various arrangements of nitrogen atoms and carbon substituents. We have also probed the mechanism of this first example of Rh(III)-catalyzed direct imidoyl C-H activation by structural characterization of a catalytically competent rhodacycle obtained after C-H activation and by kinetic isotope effects.

A novel organocatalytic activation mode of cyclopropanes is presented. The reaction concept is based on a design in which a reactive donor-acceptor cyclopropane intermediate is generated by in situ condensation of cyclopropylacetaldehydes with an aminocatalyst. The mechanism of this enamine-based activation of cyclopropylacetaldehydes is investigated by the application of a combined computational and experimental approach. The activation can be traced to a favorable orbital interaction between the π-orbital of the enamine and the σ*C-C orbital of the cyclopropyl ring. Furthermore, the synthetic potential of the developed system has been evaluated. By the application of a chiral secondary amine catalyst, the organocatalytically activated cyclopropanes show an unexpected and highly stereoselective formation of cyclobutanes, functionalizing at the usually inert sites of the donor-acceptor cyclopropane. By the application of 3-olefinic oxindoles and benzofuranone, biologically relevant spirocyclobutaneoxindoles and spirocyclobutanebenzofuranone can be obtained in good yields, high diastereomeric ratios, and excellent enantiomeric excesses. The mechanism of the reaction is discussed and two mechanistic proposals are presented.