Enantioselective reactions continued conjugate addition

In total, over the past six years, the chelating P,N-ligands have shown considerable promise in a variety of enantioselective processes, including transfer-hydrogenation and hydrosilylation of ketones, hydroboration of alkenes, conjugate addition to enones and Lewis-acid catalysed Diels-Alder reactions, in addition to those described above.128,341 It is anticipated that this list will continue to grow, and... 

In their continuing efforts on developing new NHC-catalyzed reactions, the Scheidt group reported in 2011 a diastereo- and enantioselective dimerization of enals. The desired cyclopentene products were obtained with high levels of diastereo- and enantioselectivity (up to 72% yield, >20 1 dr, 90% ee). The key element for the reactivity and selectivity of this process is the utilization of Ti(0 Pr)4, which is crucial to promote a selective 1,4-conjugate addition to another molecule of enal vs. the typical 1,2-addition which might lead to y-lactones (Scheme 7.56). 

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