3- Amino-2-nitroacrylates

The 13C- and H-NMR spectral data of a set of 2-acyl-2-nitroenamines are collected in Tables 31 and 32. The stereochemistry around C(1)=C(2) has been assigned by correlation with the NMR spectral properties of the corresponding enamines with a single electron-withdrawing group at C(2), or by comparison with compounds of fixed configuration, as those in Table 32. In the case of 3-amino-2-nitroacrylic esters (554... 

Chiara and coworkers30 could show by IR spectroscopy that the form 18Z of methyl 3-amino-2-nitroacrylates with a hydrogen bond to the nitro group exists in two conformations (B and B") with different orientations of the ester group. NMR spectra showed only two forms in ratios near 1 1, fairly insensitive to the solvent. Evidently the B -B" exchange is rapid on the NMR time-scale in the explored temperature region. The barriers to thermal Z-E rotation in these compounds fall in the range 20-27 kcal mol 151. 

Martin NJA, Cheng X, List B (2008) Organocatalytic asymmetric transferhydrogenation of heta-nitroacrylates accessing beta(2)-amino acids. J Am Chem Soc 130 13862-13863... 

Reduction of 3-nitroacrylates 43 by Saccharomyces carlshergensis Old Yellow Enzyme is the key step in the synthesis of optically pure P-2-amino acids (Scheme 2.18). High yields and enantioselectivities of the initially derived nitro-compounds 44 were achieved. The latter can be further chemically elaborated to the corresponding P-amino acids 45 [20]. 

The reduction of derivatives of a-nitroacrylic acid to amino acids follows a similar route the amine seems for a-nitro carboxylic acids to be formed partly through the oxime and partly, at a more negative potential, through another intermediate [33]. 

Yoshida developed an enantioselective Michael addition reaction of a-branched aldehydes to p-nitroacrylates by using a primary a-amino acid, L-phenylalanine (Phe-OH), lithium salt 14 (Scheme 2.9). The obtained p-formyl-p -nitroesters were transformed into the corresponding cyclic amino acids in high yields via hydrogenolysis on Pd/C. 

A modification of Hayashi s (—)-oseltamivir synthesis was recently reported by Ma et al. [64]. The group was able to replace the Michael acceptor ( )-tert-butyl 3-nitroacrylate (156) with acetyl-protected 2-amino-l-nitroethene, thereby eliminating the three-step conversion of the ester to the acetylamino group required thus far. 

SCHEME 14.12. Conjugate sulfa-Michael addition to a-substituted (3-nitroacrylates promoted by thiourea 12 and further transformation into a-thio-p -amino acids. 

The sulfa-Michael reaction to a (3,(3-disubstituted Michael acceptor, affording adducts with a new quaternary stereocenter, is usually challenging, mainly due to the low reactivity and reversibility of the process. Xiao and co-workers [41] reported that thiourea 12 promoted the highly enantioselective conjugate addition of arenethiols and substituted benzyl thiols to a-substituted (3-nitroacrylates. The enantioenriched adducts could be easily transformed into a-thio-(P -amino acids, valuable building blocks for the synthesis of p- or mixed p/a-peptides (Scheme 14.12). 

The powerful activation provided by the nitro group can even be enhanced by the presence of an additional EWG, such as an ester moiety. Accordingly, the bioreduction of ethyl (3-nitroacrylates such as 84 proceeded very efficiently with OYEl affording the optically enriched saturated (J )-nitroesters, which were employed to prepare (3 -amino acids, for example R)-86, challenging synthetic targets of undiscussed relevance in both chemistry and biology (Scheme 3.24, see Chapter 13 for further details) [105]. 

A.M., and MacMillan, D.W.C. (2009) Cycle-specific organocascade catalysis application to olefin hydroamination, hydro-oxidation, and amino-oxidation, and to natural product synthesis. Angew. Chem., Int. Ed., 48, 4349 353 (f) Martin, N.J.A., Cheng, X., and List, B. (2008) Organocatalytic asymmetric transferhydrogenation of 3-nitroacrylates accessing / -amino acids. J. Am. Chem. 

B3LYP/6-311G (PCM) calculations have shown that the 4 + 2-cycloaddition of cyclopentadiene and -/ -nitrostyrene in nitromethane solution proceeded in a stepwise mechanism. Sulfanyl-methylene-5(4//)-oxazolones and -sulfanyl-a-nitroacrylates have been used as dienophiles in the Diels-Alder reactions to synthesize norbornene/ane amino acid derivatives suitable for peptide synthesis. Organoammonium salts of chiral triamine catalyse the Diels-Alder reaction of a-(carbamoylthio)acroleins with acyclic 1,3-dienes to produce cyclohexenes with sulfur-containing chiral quaternary carbons.The helical-chiral hydrogen-donor... 

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