Hydrogenation of Acyclic Allyl and Homoallyl Alcohols

Major diastereomer Catalyst mol% Ph2 Solvent Diastereo- TOF Reference 

Entries 8-13 in Table 21.9 illustrate the effect of S-O coordination on the hydrogenation of allyl alcohols. The hydrogenation of (a-hydroxyalkyl)vinyl sul-fones follows the same stereochemical course as the corresponding acrylate via HO coordination (entries 8 and 9). However, the hydrogenation of (a-hydro-xyalkyl)vinyl sulfoxides is directed by S-O coordination, which overrides the HO-participation in the stereochemical course (entries 10-13) [56]. The directing power of S-O may be limited to vinylic examples, as compounds having the S-O and double bond in an allylic relationship failed to reduce under the standard conditions. 

The hydrogenation of acyclic homoallylic alcohols with a 1,1-disubstituted ole-fmic bond by cationic [Rh(diphos-4)]+ catalyst proceeds in modest to moderate stereoselectivity, generally forming 1,3-anti compounds (Table 21.10, entries 1, 4 and 5), and the effect of the stereogenic center at the allylic position overrides the directivity of hydroxyl group. The 1,3-syn product is then observed though in poor selectivity (entry 3) [19, 57, 58]. Inspection of the hydrogenation prod- 

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