Organoboron reagents, rhodium catalyzed

The first example of asymmetric rhodium-catalyzed 1,4-addition of organoboron reagents to enones was described in 1998 by Hayashi and Miyaura. Significant progress has been made in the past few years. This asymmetric addition reaction can be carried out in aqueous solvent for a broad range of substrates, such as a,/ -unsaturated ketones, esters, amides, phosphonates, nitroalkenes. The enantioselectivity is always very high (in most cases over 90% ee). This asymmetric transformation provides the best method for the enantioselective introduction of aryl and alkenyl groups to the / -position of these electron-deficient olefins. 

Not only organoboron reagents but also organosilicon reagents are suitable nucleophiles in the rhodium-catalyzed asymmetric 1,4-additions to a,p-enones in... 

Senda, T. Ogasawara, M. Hayashi, T. Rhodium-Catalyzed Asymmetric 1,4-Addition of Organoboron Reagents to 5,6-Dihydro-2(lH)-pyridinones. Asymmetric Synthesis of 4-Aryl-2-piperidinones. ]. Org. Chem. 2001, 66, 6852-6856. 

Recently, Hayashi reported the details of a rhodium/diene-catalyzed 1,4-addition of organoboron reagents to quinone monoketals 108, which provides a rapid access to a-arylated tetralones in high yield and stereoselectivity [94]. 

There has been only one example of a rhodium-catalyzed addition of organoboronic reagents to ketones so far. Miyaura and co-workers reported an intramolecular cy-clization of pinacol ester 77 using [RhCl(cod)]2 catalyst in the presence of potassium hydroxide, affording cyclic alcohol 78 in high yield (49) (Scheme 4.37). 

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