Enamines 3- amino-2-nitrostyrenes

The yields of nitro-1,2,3-triazoles are not usually high, but such products are useful intermediates in the preparation of many of the compounds previously discussed. For example, /3-nitrostyrenes or enamines provide routes to the 4-amino compounds that are difficult to obtain by other methods (Eqs. 10 to 12).When R = H, the yields are vastly superior. A still more promising route involves -bromo-/3-nitrostyrenes (Eq. 13). ... 

A new catalyst incorporating chiral thiourea and nucleophilic Lewis base showed efficiency in the asymmetric BH reactions. The use of a binaphthyl-based amino-thiourea catalyst 63 synthesized by Wang et al. [ 114] resulted in good yields and enantioselectivities in the reaction of cyclohexenone and aldehydes. Another amino-thiourea 12 was demonstrated as an efficient bifunctional catalyst for the enantio-selective aza-BH reaction of (3-methyl-nitrostyrene and iV-tosyl-aldimines, affording P-nitro-y-enamines in modest to excellent enantioselectivities and diastereoselec-tivities (Scheme 9.32). It was found that no reaction occurred in the absence of the methyl group of nitroalkene [115]. A similar phophine-thiourea catalyst 64 was reported in 2008 by Wu and co-workers [116] and turned out to be efficient in the asymmetric BH reaction of MVK and aldehydes, providing fast reaction rate, good yields, and excellent enantioselectivities (87-94% ee). More recently, aL-threonine-derived phosphine-thiourea catalyst 65 was readily synthesized by Lu and coworkers [117] and applied in the enantioselective BH reaction of aryl aldehyde with methyl acrylate. 

In 2011, Moreau, Greek and coworkers reported a multicatalytic process [6] merging two consecutive enamine catalytic cycles based on a Michael addition/a-amination cascade reaction [7]. The Michael addition of aldehydes to p-nitrostyrene followed by the electrophilic amination were catalyzed, respectively, by the diphenylprolinol silylether 5 and the 9-amino-(9-deoxy)-cpf-cinchonine 6 (Scheme 12.4), both previously described by Hayashi and coworkers [8] and Melchiorre and coworkers [9]. One interesting feature of this reaction is that diphenylprolinol silylether 5 can specifically catalyze the Michael addition, while 9-amino-(9-deoxy)-ep/-cinchonine 6 is required to promote the electrophilic amination. The Michael addition of propionaldehyde to p-nitrostyrene was achieved by using only 5 mol% of catalyst 5 in chloroform at 0 C. After completion of the reaction, dibenzyl azodicarboxylate (DEAD, 1.5 equiv), trifluoroacetic acid (15 mol%) and the second catalyst 6 (5 mol%) were added. The expected product 7 was obtained as a single diastereomer in good yield (80%) and with excellent enantioselectivity (ee 96%). Various nitroalkenes bearing electron-rich and electron-deficient aryl... 

Bridging the gap between organocatalysis and biocatalysis has been attained with the promiscuous enzyme 4-oxalocrotonate tautomerase (4-OT) that has been shown to catalyse the Michael-type addition of acetaldehyde to nitrostyrene. The reaction proceeds in water, affords the (5)-configured product in 89% ee, and is believed to proceed via enamine formation that employs the amino-terminal proline of the enzyme. 2 0... 

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