Diastereoselectivity

The preference for the creation of one or more diastereomers over others in an organic process is known as diastereoselectivity. Cis/trans descriptions are no longer useful when the single bond tying the two centres together is unrestrained to spin. When various allylic organometallic reagents are added to carbonyl compounds enantioselectively using chiral Lewis acids or bases or chelating ligands, the diastereoselectivity changes depending on the particular metal as follows:

(a) Si, Sn, and B allylic reagents, regardless of the initial allylic geometry, lead mostly to syn diastereoselectivity;

(b) Regardless of the initial allylic geometry, Cr, Zn, and in allylic reagents mostly produce anti diastereoselectivity;

(c) Allylic trichlorosilanes' (SiCl3) syn/anti diastereoselectivity reflects the allylic geometry's initial E/Z ratio.