Catalytic asymmetric vinylation and dienylation of ketones.J Am Chem Soc. 2005 Jun 15; 127(23):8355-61.JA
A solution to the long-standing problem of catalytic asymmetric vinylation of ketones is reported. Vinylzinc reagents are generated via hydrozirconation of terminal alkynes followed by transmetalation to zinc. In the presence of our catalyst, which is formed in situ from a bis(sulfonamide) diol ligand (1) and titanium tetraisopropoxide, the vinylzinc reagent undergoes 1,2-addition to a variety of ketones and enones with enantioselectivities (typically >90%) and high yields. This method is tolerant of functional groups, including alkyl, aryl and vinyl halides, esters, silyl protected alcohols, sulfides, and alkenes. Thus, enantioenriched tertiary allylic alcohols bearing a variety of functional groups can be prepared. It has also been found that 2,2-disubstituted vinylzinc reagents, substitution patterns not accessible through hydrozirconation, can be added to ketones with high enantioselectivities to generate trisubstituted allylic alcohols. Furthermore, we have developed an asymmetric addition of dienyl groups to ketones in the presence of our catalyst. This method enables the synthesis of dienols in high yields with enantioselectivities as high as 94%.