Chiral aminating reagent

Scheme 26 Synthesis of optically active amines 91 using the chiral amination reagent 89...

Other chiral amine reagents that have been used to effect similar stereospecific reductive aminations include 1,2-diamines and 1,2-amino alcohols (eq 5). ... 

Although the use of chiral aminating reagent in concert with chiral catalysts... 

Polymer-supported chiral amine reagents represent an attractive extension of this methodology, since these catalysts can readily be recovered (Fig. 5). Succi-nated polystyrene-divinylbenzene (17) attached to 1 promoted the addition of 6 to 7 at a slower rate than the homogeneous reaction [17]. Although the absolute configuration of the adduct (S)-8 was identical, the enantiomeric excess was low-... 

In some reactions intramolecular chalcogen nitrogen interactions may lead to stereochemical control. For example, selenenyl bromides react with C=C double bonds, providing a convenient method of introducing various functional groups. The reaction proceeds readily, but affords a racemic mixture. The modified reagent 15.22 contains a chiral amine in close interaction with the selenium atom. It reacts with olefins affording up to 97% ee of isomer A (Scheme 15.2). ... 

Nakagawa and coworkers reported a chiral ytterbium catalyst 34 which was prepared from l,l -(2,2 -bisacylamino)binaphthalene and Yb(OTf)3 in the presence of diisopro-pylethylamine by a method similar to that used for Kobayashi s chiral ytterbium reagent [52] (Scheme 1.65, Table 1.66). The amine also plays an important role in this reaction, because racemic cycloadducts were obtained without the tert-amine. Reduc-... 

A 100 MHz. proton magnetic resonance spectrum (chloroform d) of the amine in the presence of an equal amount of the chiral shift reagent, tris[3-(trifluoromethylhydroxymethylene)-d-camphorato]euro-pium(III)4 (submitters), or in the presence of an equal amount of tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium-(III) (checkers), revealed that the product contained no detectable enantiomeric isomer. 

Treatment of a chiral amine with phosgene is the cheapest way to prepare symmetrical ureas [29]. Nevertheless, due to the toxicity and reactivity of that reagent, it can advantageously be replaced by triphosgene [30] or l,l -carbonyldiimidazole [31-34] or other derivatives such as l,l -carbonyldi-2(lH)-pyridinone [35]. This procedure can be extended to thiophosgene (Scheme 1) and its thio-analogues, such as l,l -thiocarbonyldi-2(lH)-pyridinone to produce thioureas [36] chiral diamines can thus be transformed into the corresponding monoureas or monothioureas. 

Mikolajczyk and coworkers have summarized other methods which lead to the desired sulfmate esters These are asymmetric oxidation of sulfenamides, kinetic resolution of racemic sulfmates in transesterification with chiral alcohols, kinetic resolution of racemic sulfinates upon treatment with chiral Grignard reagents, optical resolution via cyclodextrin complexes, and esterification of sulfinyl chlorides with chiral alcohols in the presence of optically active amines. None of these methods is very satisfactory since the esters produced are of low enantiomeric purity. However, the reaction of dialkyl sulfites (33) with t-butylmagnesium chloride in the presence of quinine gave the corresponding methyl, ethyl, n-propyl, isopropyl and n-butyl 2,2-dimethylpropane-l-yl sulfinates (34) of 43 to 73% enantiomeric purity in 50 to 84% yield. This made available sulfinate esters for the synthesis of t-butyl sulfoxides (35). 

Zincate reagents can add to imines with or without Lewis acid catalysis. Alkylimines require BF3 but imines of pyridine-2-carboxaldehyde react directly. If the imines are derived from chiral amines, diastereoselectivity is observed. Both a-phenylethyl amine and ethyl valinate have been tried. Higher enantioselectivity was observed with mixed magnesium reagents.175... 

Based on gasliquidchromatography (GLPC) amides, formed from various enantiomeric amines and the chiral-derivatizing reagent ( S)-(—)-JV-pentafluorobenzoylprolyl-l-imidazole, could be detected at nanogram levels [43],[44]... 

Palladium(II) complexes containing orthometalated chiral amines such as those shown in Figure 7 are useful reagents ... 

Reagents derived from LiAlH4 and chiral amines have also been developed. 

Chiral amines.1 These reagents also add to imines and this reaction can be used for synthesis of optically active amines. Thus RCeCl2 adds to SAMP-hydra-zones (12, 30) to form hydrazines in good yield and high diastereoselectivity. These are reduced to optically active amines by hydrogenation catalyzed by Raney nickel. The hydrazines are prone to oxidation, but can be isolated as the stable carbamates. 

Studies of the transfer of Br+ and I+ from amine-coordinated halonium ions to acceptor l-co-alkenols have been undertaken to determine the mechanism in an effort to assist in the development of chiral transfer reagents. Transfer of Br+ and I+ from two commercially available dimeric hydroquinine and hydroquinidine ligands ((DHQ)2PHAL and (DHQD)2PHAL) to various 1, (o-alkenols and l,co-alkenoic acids is shown to provide enantiomeric excesses of 4-47% depending on the acceptor alkene. 

E. Amination of Alkenes with Chiral Borohydride Reagents. 117... 

More recently, the chiral phosphonate 85 has been used as a CDA with chiral amines to form diastereomeric phosphonic amides (86)79 which are analyzed by 31P-NMR spectroscopy for the determination of enantiomeric ratios. The reagent is readily prepared from (5)-2-butanol and phosphorous trichloride, and all a-amino acids and amines thus far examined react quantitatively in a few hours at room temperature in aqueous ethanol79. 

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