Aminohydroxylation, asymmetric

Mehrmann SJ, Abdel-MagidAF, Maryanoff CA, Medaer BP (2004) Non-Salen Metal-Catalyzed Asymmetric Dihydroxylation and Asymmetric Aminohydroxylation of Alkenes. Practical Applications and Recent Advances. 6 153-180 De Meijere, see Wu YT (2004) 13 21-58 Manage S, see Fontecave M (2005) 15 271-288... 

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. 

Figure 9 The proposed catalytic cycle of asymmetric aminohydroxylation.

As for the mechanism of asymmetric aminohydroxylation, it has been proposed that there are at least two catalytic cycles in the reaction system (Scheme 4-38).77b It is also suggested that both electronic and steric factors play important roles in the reaction. In the first cycle, in which the turnover occurs, effects of the ligand on selectivity are possible. For the ligand-independent... 

Scheme 4-38. Proposed mechanism for asymmetric aminohydroxylation. Sequence of steps in the first catalysis cycle (left) (1) addition (a1), (2) reoxidation (O), (3) hydrolysis (h1) in the second catalysis cycle (right) (1) addition (a2), (2) hydrolysis (h2), (3) reoxidation (O). The first cycle proceeds with high ee, the second with low ee. L = chiral ligand X = CH3SO2. ... 

TABLE 4-16. Influence of Ligand and Solvent on the Regioselectivity in Asymmetric Aminohydroxylation Reaction of Four Styrene Substrates7 9b... 

TABLE 4-17. Asymmetric Aminohydroxylation Using TeoCNNaCl as the Nitrogen Source... 

The catalytic asymmetric aminohydroxylation of a variety of styrene derivatives, vinyl aromatics, and some other olefins using osmium tetroxide... 

Several methods have been developed for the synthesis of the taxol side chain. We present here the asymmetric construction of this molecule via asymmetric epoxidation and asymmetric ring-opening reactions, asymmetric dihydroxylation and asymmetric aminohydroxylation reaction, asymmetric aldol reactions, as well as asymmetric Mannich reactions. 

Sharpless asymmetric aminohydroxylation can also be used for taxol side chain synthesis. For example, using DHQ as a chiral ligand, asymmetric aminohydroxylation of methyl trau.v-cinnamatc provides compound 240 in high enantiomeric excess (Scheme 7-80).37... 

Finally, osmium tetroxide-loaded, immobihzed DHQ-hgand system (28) disperses activity in the asymmetric aminohydroxylations of trans-cinnamate derivatives (Scheme 4.14) [95]. Here, the reagent system AcNHBr/LiOH was employed as nitrogen source. The immobihzed catalyst could entirely be removed by filtra-... 

There have also been significant advances in the imido chemistry of ruthenium and osmium. A variety of imido complexes in oxidation states +8 to +6 have been reported. Notably, osmium (VIII) imido complexes are active intermediates in osmium-catalyzed asymmetric aminohydroxyl-ations of alkenes. Ruthenium(VI) imido complexes with porphyrin ligands can effect stoichiometric and catalytic aziridination of alkenes. With chiral porphyrins, asymmetric aziridination of alkenes has also been achieved. Some of these imido species may also serve as models for biological processes. An imido species has been postulated as an intermediate in the nitrite reductase cycle. " ... 

Derivatization of functional groups in a natural-product scaffold can also be effectively performed on the solid-phase. An example of this is the synthesis of a small compound collection (27-compounds) based on the tetrahydroquinoline scaffold. A chiral tetrahydroquinoline scaffold was synthesized in solution from 5-hydroxy-2-nitrobenzaldehyde (Scheme 4). The synthesis involved a key asymmetric aminohydroxylation step. This building block was anchored to the solid support with a Wang linker and diversity was introduced by selective deprotection and derivatization of the protected hydroxyl and amino substituents. 

By reactions of different 13,4-triazine derivatives, C-ribosyl imidazo[2,l-/][13,4]triazines <99JCS(P1)2929> and C-ribosyl 13.4-triazolo[3,4-/ [13,4]triazines <99JCS(P1)2937> have been synthesized as inhibitors of adenosine and AMP deaminases. Catalytic asymmetric aminohydroxylation with amino substituted 13,4-triazine and 133-tiiazine derivatives, as nitrogen sources, has been described <99AG(E)1080>. 

In the asymmetric aminohydroxylation (AA) an olefin is converted into a vicinal amino alcohol by means of an osmium(VIII)-mediated suprafacial addition of a nitrogen and an oxygen atom to the double bond. Like the AD, the AA has been developed by modifying an originally stoichiometric, achiral version. Although the first aminohydroxylations were reported in 1976 [70], the asymmetric catalytic protocol is still underdevelopment [71]. 

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