Aminohydroxylation asymmetric diastereoselectivity

Another substrate class, for which the outcomes of a radical and a carbocationic process are opposite, are indoles (Fig. 85) [418], Indeed, when oxaziridines 315a or 315c were treated with indoles 314c in the presence of 2 or 10 mol% of C11CI2/ TBAC oxazolidinoindolines 316c were obtained as the exclusive products in 53-90% yield. The reaction is applicable to 2-, 3-, and 2,3-disubstituted indoles. Chiral indole derivatives acylated with (S)-proline units at nitrogen underwent asymmetric diastereoselective aminohydroxylation reactions with 86-91% de. Tricyclic hemiaminals derived from tryptamine derivatives could be transformed to pyrrolidinoindolines, which are core structures of a number of alkaloids. 

The first examples of the diastereoselective aminohydroxylation of chiral acryl amides, R3CH=C(R2)CONHCH (Me)R1, have been reported. The reaction is believed to proceed within the so-called second catalytic cycle with diastereoisomeric excesses (g) reaching >99 1. The reaction relies solely on the stereochemical information provided by the enantiomerically pure starting materials. A stereochemical model for the observed asymmetric induction has been proposed.128... 

The Sharpless regioreversed asymmetric aminohydroxylation protocol was used as a key step in the total synthesis of ustiloxin D by M.M. Joullie and co-workers.The ( )-ethyl cinnamate derivative was subjected to in situ generated sodium salt of the N-Cbz chloroamine in the presence of catalytic amounts of the anthraquinone-based chiral ligand to afford the desired A/-Cbz protected (2S,3R)-(3-hydroxy amino ester in good yield and with good diastereoselectivity. 

The mnemonic device used to predict the sense of enantioselectivity in the AD reaction can also be used in the AA process. Typical examples include the asymmetric aminohydroxylation of alkenes (5.63-5.67), all with excellent enantioselectivity. Heterocyclic groups are tolerated in the AA reaction and high ees have been obtained for the aminohydroxylation of furanoyl acrylates such as (5.65). ° In common with the AD reaction, pyrrolyl- and pyridyl-substituted olefins are difficult substrates and blocking of the nitrogen is required for enantioselective aminohydroxylation. However, indoles such as (5.66) undergo aminohydroxylation with good ee. The AA reaction has also been applied to the desymmetrisation of dienylsilane (5.67) by Landais and coworkers. Whilst the enantioselectivity is not perfect, the reaction is still remarkably regio- and diastereoselective. 

Olefins have a rich history in organic chemistry and consequently there is a vast array of transformations available to this fundamental functional group. This chapter discusses the classic methods for stereoselective oxidations of olefins, spanning the range from diastereoselective [16-18] and enantioselec-tive [19-29] formation of epoxides to their asymmetric ring-opening reactions [30-33], stereoselective formation of aziridines [34—37], iodolactoniza-tions and other olefin cyclizations induced by electrophiles [38, 39], dihy-droxylations [40-49], and aminohydroxylations [47, 50] (Figure 9.1). 

---