Transition Metal Catalysis

This review comprises two major parts, which have chiral metal-enolates in their focus. In the first part, we discuss transition metal catalyzed conjugate additions leading to chiral enolates, which are then subsequently functionalized by reactions with electrophiles, both further catalyzed or uncatalyzed. The second part deals with base generated enolates and their use in the asymmetric transition metal catalyzed processes.

D. Vargová, I. Némethová, K. Plevová, R. Šebesta, ACS Catal. 2019, 9, 3104-3143; DOI: 10.1021/acscatal.8b04357.
Asymmetric conjugate addition of organozirconium species to N-heterocyclic Michael acceptors is presented in this paper. High yield of products was obtained with α,β-unsaturated lactams which are highly unstable, that is why enantioselectivity did not surpass 64% ee. On the other hand protected 2,3-dihydropyridine-4(1H)-ones provided in the same catalytic system desired products in low yields but in enantioselectivity up to 84% ee.

I. Némethová, S. Bilka, R. Šebesta, J. Organomet. Chem. 2018, 856, 100-108; DOI: 10.1016/j.jorganchem.2017.12.042.
In this paper we present first Zr-enolate trapping, initiated by Cu-catalysed CA, by naked organic cations and also by other Michael acceptors. The enantioselective version of this reaction was studied as well, unfortunately the yields of the trapping products were rather low, due to the low reactivity of intermediate species.

I. Némethová, Z. Sorádová, R. Šebesta, Synthesis, 2017, 49, 2461-2469; DOI: 10.1055/s-0036-1588968.www.thieme-connect.com/products/ejournals/abstract/10.1055/s-0036-1588968
Picture
We are interested in these reactions with Grignard reagents as nucleophiles for conjugate addition to produce chiral magnesium enolates. As electrophile we choose:
Preparation of silylated ferrocenyl derivatives we enabled through Retro-Brook rearrangement on O-silylated ferrocenyl alcohol initiated by Br-Li exchange. [see Chem. Eur. J. 2015, 21, 13445-13453]