Cinchona aminohydroxylation

Most remarkably, catalytic aminohydroxylation of cinnamate amides with sulfonamides in the absence of cinchona alkaloid ligands showed a remarkable chemoselectivity in favor of amino alcohol formation [75]. 

A vincinal amino alcohol grouping is present in a fair number of natural products which possess useful biological activity, such as antibiotics122. Such a functionality has been produced from alkenes via osmium-mediated aminohydroxylation (equation 22)123. The reaction proceeds in 40-97% yield and is enantioselective if chiral osmium-Cinchona alkaloid complexes are used to mediate the reaction. 

Keywords Asymmetric aminohydroxylation, Osmium tetroxide, Cinchona alkaloid, Ligand-accelerated catalysis, Immobilization, Abbreviations... 

Sharpless and co-workers first reported the aminohydroxyIation of alkenes in 1975 and have subsequently extended the reaction into an efficient one-step catalytic asymmetric aminohydroxylation. This reaction uses an osmium catalyst [K20s02(OH)4], chloramine salt (such as chloramine T see Chapter 7, section 7.6) as the oxidant and cinchona alkaloid 1.71 or 1.72 as the chiral ligand. For example, asymmetric aminohydroxylation of styrene (1.73) could produce two regioisomeric amino alcohols 1.74 and 1.75. Using Sharpless asymmetric aminohydroxylation, (IR)-N-ethoxycarbonyl-l-phenyl-2-hydroxyethylamine (1.74) was obtained by O Brien et al as the major product and with high enantiomeric excess than its regioisomeric counterpart (R)-N-ethoxycarbonyl-2-phenyl-2-hydroxyethylamine (1.75). The corresponding free amino alcohols were obtained by deprotection of ethyl carbamate (urethane) derivatives. 

Aminohydroxylations. Several carbamates HjNCOOR (R = Et, t-Bu, CljCI ), the corresponding A-chloro-iV-sodio derivatives, and A-bromoacetamide have been employed as nitrogen source in the reaction mediated by bis-cinchona alkaloid ligand complexed osmate. The products are readily manipulated to give two pairs of chiral diamines. In one version the cinchona alkaloid derivatives are linked to silica gel surface through thiopropyl chains. ... 

Catalytic asymmetric aminohydroxylation using Os(VIII) and Sharpless cinchona alkaloid ligand has been applied to a,p- and P,Y-unsaturated phosphonate substrates (Scheme 48). The reaction only works for the aryl substituted examples (287) and although initial e.e. s are sometimes low, they can be increased to >90% by a single recrystallisation. The phosphonic acid analogue... 

Most of the polymeric-catalytic systems used for the dihydroxylation or aminohydroxylation of C=C bond is issued from alkaloid, mainly cinchona which has been proved to be the best ligand for this type of reaction. 

A ligand-independent, osmium-catalyzed aminohydroxylation of MBH adduct has been developed by Sharpless et al. (Scheme 3.202). The yield, rate and selectivity of this reaction are not affected by the addition of cinchona alkaloid ligands. The diastereoselectivity for the aminohydroxylation is influenced by the aldehyde-derived substituent, while the acrylate-derived substituent has a minimal effect. Various derivatives and close analogs of the MBH product-core failed to aminohydroxylate, emphasizing the unique reactivity of this class of olefins. 

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