Asymmetric aminohydroxylation chloramine

Subsequently, stoichiometric asymmetric aminohydroxylation was reported.78 Recently, it was found by Sharpless79 that through the combination of chloramine-T/Os04 catalyst with phthalazine ligands used in the asymmetric dihydroxylation reaction, catalytic asymmetric aminohydroxylation of olefins was realized in aqueous acetonitrile or tert-butanol (Scheme 3.3). The use of aqueous rerr-butanol is advantageous when the reaction product is not soluble. In this case, essentially pure products can be isolated by a simple filtration and the toluenesulfonamide byproduct remains in the mother liquor. A variety of olefins can be aminohydroxylated in this way (Table 3.1). The reaction is not only performed in aqueous medium but it is also not sensitive to oxygen. Electron-deficient olefins such as fumarate reacted similarly with high ee values. 

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. 

Miscellaneous Reagents. Chloramine-T/Osmium Tetroxide. The Sharpless asymmetric aminohydroxylation system for olefins (4-MeC6H4S02N(Na)Cl/ OsCVcinchona alkaloid derived catalysts)340,341 converts silyl enol ethers into a-(p-tosylamino) ketones in 34-40% yield and 76-92% ee (see Eq. 99).342... 

Since excellent results were obtained in the asymmetric aminohydroxylation in homogeneous phase by Sharpless [169], heterogeneous systems appeared to be of great interest. Nandanan has reported the first heterogeneous osmium tetroxide-catalyzed asymmetric aminohydroxylation of various olefins using polymer-supported bisdehydroquinine ligand 273 (Scheme 111) [170]. When chloramine T was used as nitogen source, yields and ee were moderate with all olefins. 

Amino-Hydroxylation. A related reaction to asymmetric dihydroxylation is the asymmetric amino-hydroxylation of olefins, forming v/c-ami noalcohols. The vic-hydroxyamino group is found in many biologically important molecules, such as the (3-amino acid 3.10 (the side-chain of taxol). In the mid-1970s, Sharpless76 reported that the trihydrate of N-chloro-p-toluenesulfonamide sodium salt (chloramine-T) reacts with olefins in the presence of a catalytic amount of osmium tetroxide to produce vicinal hydroxyl p-toluenesulfonamides (Eq. 3.16). Aminohydroxylation was also promoted by palladium.77... 

---