Hydrazines, asymmetrically substituted

Hydrazine hydrate, in preparation of sulfonylhydrazides, 40, 93, OS in reduction of 2-nitrofiuorene to 2-aminofluorene, 40, 5 in Wolff-Kishner reduction, 43, 34 Hydrazines, asymmetrically substituted by N-aminatiou of amines by hydroxylamine-O-sulfonic acid, 43,2... 

Asymmetrically substituted hydrazines can be converted to N-nitro-soamines by reaction with nitrous acid. They can be detected by using the Liebermann reaction (p. 195). 

Scheme 6.81 Transformation of one adduct prepared from the 64-catalyzed asymmetric addition of a-substituted P-keto esters to di-tert-butyl azodicarboxylate (a-hydrazination) into the corresponding oxazolidinone amino acid derivative.

An efficient asymmetric synthesis of the 3-substituted /3-sultams 163 has been reported. The key step of the synthesis is the Lewis acid-catalyzed aza-Michael addition of the enantiopure hydrazines (A)-l-amino-2-methoxy-methylpyrrolidine (SAMP) or CR,l ,l )-2-amino-3-methoxymethyl-2-azabicyclo[3.3.0]octane (RAMBO) to the alke-nylsulfonyl sulfonates 176. /3-Hydrazino sulfonates were obtained in good yield and excellent enantioselectivity. Cleavage of the sulfonates followed by chlorination resulted in the corresponding sulfonyl chlorides 177. The (A)-3-substituted /3-sultams 163 have been obtained in moderate to good yields and high enantioselectivity over two steps, an acidic N-deprotection followed by in situ cyclization promoted by triethylamine (Scheme 55) <2002TL5109, 2003S1856>. 

Methods for the preparation of hydrazones and oximes differ little from those used for the synthesis of imines from ketones and aldehydes in that the appropriate nitrogen species and the ketone are mixed. However, the equilibrium for the majority of reactions of ketones and aldehydes with hydrazines and hy-droxylamine favor the product hydr nes and oximes and removal of the water formed by the condensation is not required. 8(> Acid catalysis is complicated by the basicity of the reagent and, for example, the maximum rate of oxime formation is at approximately pH 4. Complicating reactions can occur such as the 1 2 combination of hydrazine with two ketones or aldehydes to form azines but this is not a problem with the substituted hydrazines that are used for asymmetric induction. 

Asymmetrically disubstituted hydrazines can be obtained by reduction of nitrosamines. Singly substituted hydrazines can be prepared, in principle, analogously through the intermediacy of alkylnitrosoureas. These reductions are usually carried out by zinc in acetic acid if mineral acid is used the nitroso group is split off. The method goes back to work by Emil Fischer.124... 

Chiral bipyridine ligands have been explored for the asymmetric cyclopropanation of diazoacetate. For example, Lyle and Wilson reported that optically active C2-symmetric 2,2 -bipiridyl 248 served as a good ligand for asymmetric cyclopropanation in the presence of CuOTf and phenyl hydrazine (Scheme 1.116) [173]. Boyd et al. showed that a similar 2,2 -bipyridyl 249 also worked as an effective catalyst (Scheme 1.117) [174]. Mono-oxazoline-substituted 2,2 -bipyridyl derivatives 250-252 have been examined (Scheme 1.118) [175]. Chiral double helical oligopyridine... 

Shibata and coworkers [135] described the asymmetric phase-transfer catalytic synthesis of trifluoromethyl-substituted 2-isoxazolines 100 by an enantioselective conjugate addition of hydroxylamine to trifluoromethylated enones 99 and subsequent intramolecular formation of the imine, whereas Briere et al. [136] developed a facile method for the straightforward enantioselective synthesis of 3,5-diaryl pyrazoHnes 102 by phase-transfer-catalyzed conjugate addition of N-Boc-hydrazine... 

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