Hydration asymmetric olefins

Wacker olefin oxidation, which is depicted in its simplest form in Eq. (6.33), contains palladium( 11)-catalyzed hydration of olefin in its important step (Eq. 6.34) and is discussed extensively [62]. In this review article we introduce two asymmetric Wacker type reactions. 

Asymmetric olefins, which carry more alkyl substituents at the Ce center than at the Ca center, are also hydroborated by the unhindered BH3 with considerable regioselectivity (Table 3.1). After oxidative workup, one isolates the alcohol in the a position almost exclusively. According to what has already been stated, as the more bulky reagent, 9-BBN reacts with more sensitivity to steric effects than BH3 and its secondary products. It therefore makes possible olefin hydrations with almost perfect regiocontrol. 

Stereoselective Hydration of Asymmetric Olefins and Substrate Control of the Stereoselectivity... 

Fig. 3.38. Regioselective hydration of an asymmetric olefin via solvomercuration/reduction.

The first catalytic asymmetric Michael addition of an mygen-centred addition of salicylaldoxime to a,p-unsaturated imides was achieved by the Jacobsen group in 2004 (Scheme 19.34). With p-oxo dimer catalyst [r,R)-[(salan)Al]20 5 as the catalyst, a series of a,p-unsaturated imides worked well. It should be noted that this method could tolerate ester, acetal, and silyl ether functionality, allowing its potential application as an acetate aldol alternative in polyketide natural product synthesis. When combined with efficient N-O bond hydrogenolysis, this (salen)aluminium-catalysed reaction enables the net enantioselective hydration of electron-deficient olefins with no need for purification of the intermediate oxime ethers. 

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