Chiral nitrogen transfer

A-Aminophthalimide (118) can also be added to olefins in an asymmetric fashion. Thus, reaction of A -enoyl oxazolidinone 122 with 118 and lead tetraacetate in the presence of the camphor-derived chiral ligand 120 provides aziridine 123 in 83% yield and with 95% ee <020L1107>. Other useful chiral ligands include imine 121, derived from the condensation of 2,2 -diamino-6,6 -dimethylbiphenyl with 2,6-dichlorobenzaldehyde. The corresponding monometallic Cu(I) complex was found to be very efficient in chiral nitrogen transfer onto chromene derivative 124 using (Ar-(p-toluenesulfonyl)imino)phenyliodinane (PhI=NTs) to provide aziridine 125 in 87% yield and 99% ee <02JOC3450>. 

Aziridines have been prepared stereospecifically by the nucleophilic addition of the nitrogen residue to alkenes <80T73). Introduction of the nitrene is accomplished readily via a Michael-type addition with free diphenylsulfilimine (Scheme 12), and where a chiral sulfilimine is used the chirality is transferred to the aziridine with optical yields in excess of 25%. 

Later, Carreira et al. reported that nitrido-Mnv(salen) also underwent a nitrogen-transfer reaction under similar reaction conditions.142 An asymmetric version of this reaction has been realized by using the chiral nitrido-Mnv(salen) (44) (Scheme 32).143 When trifluoroacetic acid... 

Dehmlow and coworkers [17] compared the efficiency of monodeazadnchona alkaloid derivatives 14a-c in the enantioselective epoxidation of naphthoquinone 50 with that of cinchona alkaloid-derived chiral phase-transfer catalysts 15a-c (Table 7.7) (for comparison of the alkylation reaction, see Table 7.1). Interestingly, the non-natural cinchona alkaloid analogues 14a-c afforded better results than natural cinchona alkaloids 15a-c. The deazacinchonine derivatives 14a,b produced epoxidation product 51 in higher enantioselectivity than the related cinchona alkaloids 15a,b. Of note, catalyst 14c, which possessed a bulky 9-anthracenylmethyl substituent on the quaternary nitrogen, afforded the highest enantioselectivity (84% ee). 

If nitrogen is included in a chiral auxiliary, chirality is transferred with excellent enantiomeric excesses to the new C-C bond formed. Thus, alcohols are prepared with excellent enantioselectivity after oxidative cleavage of the Si-C bond, and a chiral 1,3-diol is obtained with high optical purity.297,298... 

Several families of efficient chiral phase transfer catalysts are now available for use in asymmetric synthesis. To date, the highest enantiomeric excesses (>95% ee) are obtained using salts derived from cinchona alkaloids with a 9-anthracenylmethyl substituent on the bridgehead nitrogen (e.g. lb, 2b). These catalysts will be used to improve the enantiose-lectivity of existing asymmetric PTC reactions and will be exploited in other anion-mediated processes both in the laboratory and industrially. 

Since a chiral nitride complex is considered to be a good candidate for an asymmetric nitrogen transfer reagent, the intention of the authors group was to apply some complexes to asymmetric organic synthesis [22]. 

The chiral nitridomanganese complex 545 represents a novel self-contained asymmetric nitrogen-transfer reagent which has been used to convert alkenes to scalemic aziridines directly, although a stoichiometric amount of transfer reagent is required. This protocol makes use of A -2-(trimethylsilyl)ethanesulfonyl chloride (SESCl) (546) as an activator, providing A -SES-aziridines 547 that are easily deprotected under mild conditions using... 

The addition of oxygen across the C—N double bond is a common and synthetically useful process. The product oxaziridines are of interest for theoretical reasons (largely due to the high configurational stability of the chiral nitrogen), as reagents (such as oxygen transfer moieties), and as synthetic intermediates. The stereochemical aspects of oxaziridine synthesis and reactivity have been reviewed. ... 

Significantly increased ee values were obtained by using the new chiral PTCs 31 and 32, which can be easily prepared starting from 2-hydroxy-3-chloromethyl-5-methyl benzaldehyde and cinchonine or cinchonidine, respectively [30]. By using 31 or 32, up to 95% ee was achieved in the reaction of electron-deficient olefins with N-acyl-N-arylhydroxylamines as nitrogen transfer reagents under biphasic conditions (toluene/aqueous NaOH) at room temperature (Scheme 5.24). 

Nitrogen Transfer Catalyzed hy Chiral Metal Complexes. 11... 

Nitrogen Transfer Catalyzed by Chiral Metal Complexes... 

As the cinchona alkaloids contain a nucleophilic nitrogen center, they can be alkylated at this position. Thus, cinchonidine reacts with benzyl chlorides to form quaternary salts, e.g., 9 and 108, which are useful as chiral phase-transfer catalysts (see Section D.1.5.2.4. for enantioselec-tive additions to azaenolates, and D.4.1. for the oxidation of enolates). Further modification by catalytic reduction of the double bond (hydrogen/platinum) leads to the corresponding dihydrocinchonidine derivatives. 

Chiral Nitrogen Donor Ligands (Amines and Oxazolines). 1,2-Diphenyl-ethylenediamine (DPEN (56)) and its alkylated and tosylated derivatives, as well as 1,2-cyclohexane-diamine (CHDA (57)) based ligands proved to be applicable in a range of asymmetric reactions (Fig. 7), especially in enantioselective transfer hydrogenations providing ees more than 90% for acetophenone as substrate. Crucial steps of this reaction are the irreversible deprotonation of the ligand... 

In addition, chiral nitrogen-substituted quaternary stereocenters can be accomplished by using 1,3-dicarbonyliccompounds as substrates in the direct a-amination process. Thus, several cyclic (i-ketoesters 46 (Scheme 27.9) were submitted to electrophilic amination under phase-transfer conditions catalyzed by the chiral binaphthyl phosphonium salt 47 [50a], Different substituents on the aromatic ring were tolerated, but lower yields were obtained using a six-membered ring cyclic... 

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