Allylic alcohols site selectivity

The ethers clearly do not interfere with the selective reaction by providing an alternative site for reagent coordination, a problem that will be addressed again later in the section on asymmetric catalysis. Cyclic allylic alcohols are cyclopropa-nated with high selectivity as well (Table 3.8, entry 8). 

These results should be interpreted in terms of the different accessibility of the organic molecule to the active sites and of differences in the metal size. However, it is worth noting that using Ru supported on these molecular sieves, it is possible to reach a 100% diastereomeric excess in the (1 IS, 15R) form for about 80% selectivity to allyl alcohol. These results also indicated the fact that the reaction is very sensible to the solvent nature. Methanol was found to enhance the reaction rate compared with THF or ethanol. 

Site selectivity with allylic alcohols and amines. 836... 

Adam and coworkers reported the regioselective and diastereoselective formation of oxetanes during the PB reaction of allylic alcohols (Scheme 7.27) [43, 44]. This group proposed that hydrogen-bond interactions in the exciplex played an important role in controlling the selectivity. D Auria and coworkers also observed a site-selective and diastereoselective formation of oxetanes in the PB reaction of 2-furylmethanol derivatives (Scheme 7.27) [45]. 

A major limitation to the Sharpless-Katsuki epoxidation is that its utility is largely confined to oxidation of allylic alcohols. Homoallylic alcohols are oxidized less cleanly and the oxidation of simple olefins shows little enantio-selectivity. This is presumably because the stereochemical control depends on anchoring the substrate to a particular site on the metal by means of an auxiliary coordinating function. 

Propylene oxide isomerized over silica-magnesia and other oxides to give propionaldehyde and acetone on acidic and basic sites, respectively, and allyl alcohol on acid-base bifunctional catalysts. Methylvinyl ketone was formed selectively in the reaction of acetone and methanol with oxygen over silica-magnesia. Tanabe and co-workers have studied the alkylation of phenol... 

A comparison of the ratio of l-d 3,3-d2-acrolein formed from the reaction of bl-dj-allyl alcohol with Bi2O3 3MOO3 in the presence of pyridine (reaction only on acrolein-forming sites) and for the corresponding reactions of a 50 50 mixture of 1,1 3,3-d2-allyl alcohol and Ul-dj-propylene (Table IV) shows that only the 50 50 mixture produces the ratio observed for propylene-hl-dj. In terms of the mechanism for selective propylene oxida-... 

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