Acids aminohydroxylations

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... 

The precursor tripeptide 96 (Scheme 19) was obtained in three steps from the constituent amino acids. These were obtained using the Sharpless aminohydroxylation proce-... 

Conceptually interesting is the discovery that products obtained by the aminohydroxylation itself can serve as ligands [23], Thus, the AA of styrenes 28 proceeds in high yields to the regioisomeric amino alcohols 29 and 30 in the presence of catalytic amounts of 31, being the AA product of cinnamic acid, with moderate, nevertheless significant enantioselectivity. 

The recent development of the Sharpless ami-nohydroxylation [2] makes it possible to synthesize an amino alcohol in both optical antipodes (Fig. 2). For example, starting from 2-vinyl-naphthalene (5), the amino alcohol 6 is readily synthesized by the aminohydroxylation protocol [3]. After deprotection, the free amino alcohol 8 was coupled with dimethylmalonic acid di-... 

Key step of the synthesis of compound 15, a derivative of amino acid 6, is an asymmetric Sharpless aminohydroxylation. The central building block 16 (amino acid 4), however, was built up from 4-aminobenzoic acid by an asymmetric dihydroxylation (AD) in 12 steps. Coupling of the biaryl fragment 19 with the corresponding amino acid derivatives (Scheme 6) gave tripeptide 20. By treatment with CuBr SMc2, K2CO3 and pyridine in acetonitrile under re-... 

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... 

The aziridino alcohols that have been prepared and tested as chiral promoters for the catalytic asymmetric dialkylzinc alkylation of imines are shown in Fig. 4. The authors have investigated three different approaches to obtain the ligands in enantiomerically pure form (1) the use of the chiral pool, (2) the Sharpless asymmetric aminohydroxylation, and (3) the Sharpless asymmetric dihydroxylation. The starting materials for the preparation of the aziridino alcohols 30, 31a-h, 32a,b, and 33 were the readily available amino acids L-serine, L-threonine, and aZZo-L-threonine. 

Sharpless catalytic asymmetric aminohydroxylation (AA) provides a direct and efficient route to the taxol side chain as well as a number of other natural products and synthetic ligands. The required asymmetry of the taxol side chain was controlled by (DHQ)2-PHAL, and hydroxyla-tion was achieved with potassium osmate (K20s02(0H)4). Various N-haloamide salts were investigated, and yields and percentage ee were good to excellent under different conditions. For example, reaction of methyl cinnamate under Sharpless catalytic AA conditions gave (2R,3S) N-tosyl-3-phenyl isoserine 7.3.1 in 82% ee in 69% yield. Compound 7.3.1 was then converted to the taxol side chain acid in two steps in good yield (262). 

Scheme 7.31 Acid-promoted aziridination and formal aminohydroxylation of electron-...

The metal-free intramolecular 5 Nf-exo-trig aminohydroxylation of Al-alkenyl-sulfonamides (81) can be effected by oxone activated with Brpnsted acid as catalyst. The reaction thus proceeds via (83) and affords the prolinol derivatives (82). Although the scheme suggests that the reaction should be diastereoselective, this issue has not been addressed and there is also an incorrect use of curly arrows in this paper. 

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