Addition of organozincs

Design of chiral catalysis and asymmetric autocatalysis for diphenyl-(l-methyl-pyrrolidin-2-yl) methanol-catalyzed enantioselective additions of organozinc reagents 97YGK994. 

Scheme 2.30 Copper-catalysed asymmetric conjugate addition of organozincs to enones...

Even if hundreds of chiral catalysts have been developed to promote the enantioselective addition of alkylzinc reagents to aldehydes with enantioselectivities over 90% ee, the addition of organozinc reagents to aldehydes is not a solved problem. For example, only very few studies on the addition of vinyl groups or acetylides and even arylzinc reagents to aldehydes have been published, in spite of the fact that the products of these reactions, chiral allylic, propargylic and aryl alcohols, are valuable chiral building blocks. 

In 1998, two other examples of chiral ligands that enabled the asymmetric addition of organozinc reagents to ketones were reported by two groups independently. Thus, Dosa and Fu employed the nonsulfur-containing Noyori s DAIB " ligand in the asymmetric addition of ZnPh2 to ketones with... 

Addition of Organozinc Reagents to Aldehydes, Ketones, and a-Ketoesters 383... 

Addition of Organozinc Reagents to Aldehydes, Ketones, and a-Ketoesters 2.06.16.2.1 Chiral ligands used in addition reactions of diorganozincs with aldehydes... 

A theoretical study of the reaction mechanism for addition of organozincate complexes to aldehydes was recently performed using density functional theory.298 It has been suggested that the addition takes place through formation of a four-centered transition state and, therefore, it can be considered a typical nucleophilic reaction. 

Catalytic properties of external chiral additives such as (2S,3/ )-4-dimethyl-amino-l,2-diphenyl-3- methyl-2-butoxide (A 16) (574, 575) and 2-magnesium-3-zinc salts of dialkyl (f ,f )-tartrate (A17) were employed in the highly stereoselective addition of organozinc reagents to derivatives of 3,4-dihydro-isoquinoline-A-oxide (Scheme 2.147) (576). 

TADDOL 104 and 126 afford 95-99% ee in the asymmetric addition of organozinc reagents to a variety of aldehydes. The best enantioselectivities are observed when a mixture of the chiral titanium TADDOL compound 127 and excess [Ti(OPr1)4] are employed (Scheme 2-49). The mechanism of the alkylzinc addition involves acceleration of the asymmetric catalytic process by the... 

---