Alkenes hydroxy directing effect

Another often used chiral ligand is l,F-binaphthyl-2,2 -diyl-bis(phosphine), or binap.It can be built into ruthenium catalysts, which display high activities and enantio-selectivities for the hydrogenation of alkenes, amines, allylalcohols, and unsaturated carbonyls. A directing effect is observed for an a-hydroxy group in these cases. 

Using Simmons-Smith type reagents, hydroxy and alkoxy groups in the allylic or homoallylic position exhibit a very strong syn-directing effect on methylene transfer, which usually overrides the steric influence of further substituents in an alkene2,5 (see Table 2 for the transformation of simple cyclic alkenes)29 32. 

In 1984 Fujisawa et al. observed a directing effect due to a CT oxygen stereocenter (Scheme 4.29) [32]. Tandem deprotonation and silylation of the j8-hydroxy allylic ester presumably gave the intermediate sUyloxy silyl ketene acetal. The Z-config-uration of the silyl ketene acetal was a consequence of chelation of the intermediate dianion by the Id cation. The authors postulated that the allylic alkene prefer-... 

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