Rhodium conjugate arylation

Figure 8.10 Suitable acceptors for rhodium/diene-catalyzed conjugate arylation.

Rhodium-Catalyzed Enantioselective Conjugate Arylation-Protonation... 

Scheme 8.39 Rhodium-catalyzed conjugate arylation-aldol cyclization.

Rhodium-Catalyzed Conjugate Arylation-Aldol-Addition... 

Feringa recently reported a highly enantio- and diastereoselective one-pot conjugate arylation/allylation sequence (Scheme 8.42) [120] where the initial rhodium/ phosphoramidite-catalyzed conjugate addition of arylboronic acids in dioxane/ water was complemented by a Barbier-type indium-mediated allylation. 

Scheme 8.42 Rhodium-catalyzed conjugate arylation-allylation.

Scheme 21 Conjugate arylation of a, -unsaturated ketones by rhodium-catalyzed -carbon elimination from unstrained tert-alcohols...

Rhodium Conjugate addition of aryl boronic acids to cyclohex-2-enone, catalysed by [Rh(diene)(OH)]2 complexes, afforded the corresponding product with the following enantioselectivities 96% ee with (508) ligand, 83% with (509), and 90% with (510). DFT calculations were used to shed light on the transition state structures and energies. " The sulfoxide-olefin ligand (511) exhibited >99% ee " ... 

This catalytic reaction was believed to proceed analogously to those with phenylboronic acids (Scheme 49) 137 137a Transmetallation of the arylstannane with the cationic rhodium complex generated the rhodium aryl species a and trimethyltin tetrafluoroborate. Conjugate addition generated rhodium enolate b, which subsequently reacted with... 

It is worth noting that conjugate addition can also be effected by the addition of aryl- and alkenylboronic acid reagents to enones in the presence of rhodium catalysts. This new catalyst system has the following advantages ... 

The use of organosilanes for rhodium-catalyzed conjugate addition is also feasible. In 2001, Mori reported that the catalytic conjugate addition of aryl(ethyl)silanediols to a,f -unsaturated carbonyl compounds takes place in the presence of [Rh(OH)(COD)]2 in a... 

Oi and Inoue recently described the asymmetric rhodium-catalyzed addition of organosilanes [35]. The addition of aryl- and alkenyltriaUcoxysilanes to u,y9-unsaturated ketones takes place, in the presence of 4 mol% of a cationic rhodium catalyst generated from [Rh(COD)(MeCN)2]BF4 and (S)-B1NAP in dioxane/H20 (10 1) at 90°C, to give the corresponding conjugate addition products (Eq. 3). The enantioselectivity is comparable to that observed with the boronic acids, as the same stereochemical pathway is applicable to these reactions (compare Scheme 3.7). 

Complementary to the use of zinc reagents for the introduction of (functionalized) alkyl groups is the rhodium-catalyzed conjugate addition of aryl- and alkenylboron reagents. This method rapidly became popular, also because arylboron reagents are air and moisture stable and a large variety of them is commercially available . 

Rhodium complex 27 has also been successfully applied in the enantio-selective conjugate addition of arylboronic acids [59]. In the synthesis of the 4-amino-3-aryl-butyric acid derivative 28, Helmchen et al. found that the addition product was obtained in > 99% ee (59% yield) within 2 h at 65 °C, whereas previous attempts with (S)-BINAP and [Rh(acac)(C2H4)2]... 

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