Homoallyl alcohols homogeneous hydrogenation

Homogeneous hydrogenation of chiral allylic and homoallylic alcohols is accomplished with a high degree of diastereoselectivity, as shown in the hydrogenation of 3-phenylbut-3-en-2-ol (14) and 4-phe-nylpent-4-en-2-ol (16) in the presence of (15). ... 

Figure 4.6. Internal asymmetric induction in homogeneous hydrogenation of allylic and homoallylic alcohols.

Evans conducted a study of directed homogeneous hydrogenations of a series of acyclic homoallylic alcohols, as illustrated below [55]. The observed stereochemical outcome of the reductions is consistent with a directed process that is believed to proceed through transition state structures 72 (Equation 16) and 75 (Equation 17). The facile installation of a methine stereo-genic center by directed hydrogenation to give 78 (dr=94 6) was elegantly showcased in Evans synthesis of the polyether antibiotic ionomycin (79, Scheme 8.9) [56]. 

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