Gennadii V. Shustov

Conformation and circular dichroism of some N-nitropyrrolidines

The results of a theoretical investigation (ab initio calculations) of the parent nitropyrrolidine 1 and its (R)-2-methyl and (R,R)-2,5-dimethyl derivatives 2, 3 are in good agreement with the CD, UV and 1H NMR spectra of 2, 3 and the X-ray analysis of 3. In the ground state of nitropyrrolidines l, 2 both nitrogen atoms of the nitroamino group are pyramidal and both nitrogen atoms of 3 are planar. In all cases, a small twisting of the nitroamino group about the N–N bond is observed. An envelope conformation with the C4 atom at the tip is predicted for nitropyrrolidine 1 and the more stable isomer 2a, which has a pseudoaxial methyl group. The less stable isomer 2b, (with a pseudoequatorial methyl group) and both isomers of 3 (2,5-di-pseudoaxial 3a and 2,5-di-pseudoequatorial 3b) adopt a half-chair conformation. In solutions and the crystal state, 3 exists as isomer 3a. Four Cotton effects are observed in the CD spectra of 2, 3. The signs of the Cotton effect at 270, 240 and 200 nm (the no+–π*, πN–π* and πo–π* electronic transitions) are determined by the configuration of the α-carbon chiral centres. The intrinsic chirality of the nitroamino chromophore and the chirality of the five-membered ring influence, mostly, the Cotton effect of the no––π* transition at 300 nm.

Chiroptical properties of the inherently non-planar nitroamine chromophore in N-nitroaziridines

The long-wavelength Cotton effect (CE) of the nitroamine chromophore is very sensitive to structural non-planarity and nelicity; the sign of this CE for N-nitroaziridines has the same connection with the intrinsic chirality of the chromophore as m the case of N-acyl-, N-nitroso-aziridines and aziridinones.

Chiroptical properties of the non-planar nitrosamine chromophore in N-nitrosaziridines

The sign of the long-wavelength Cotton effect in the circular dichroism (CD) spectra of N-nitrosaziridines, possessing a non-planar nitrosamine chromophore, is determined by the intrinsic chirality of the chromophore, as in the cases of N-acylaziridines and gauche-cyclopropylketones.

Topomerization of substituted 1-amino- and 1-oxy-Δ2-1,2,3-triazolines

For 1-amino- and 1-oxy-Δ2-1,2,3-triazolines, retardation (on the NMR time scale) is observed for rotation around the exocyclic N-N or N-O bond; the measured barriers to topomerization amount to 8.3–13.8 kcal/mole.

Geminal systems. 50. Solvolysis of 1-tosyloxy-Δ2-1,2,3-triazoline-5,5-dicarboxylate esters and the structure of the solvolysis product, O-tosyl-N-α,α-bis(ethoxycarbonyl)-β-methoxyethylhydroxylamine

Solvolysis of 1-tosyloxy-Δ2-1,2,3-triazoline-5,5-dicarboxylic acid esters (1) occurs via elimination of N2 and leads predominantly to N-β-hydroxylethyl-O-tosylhydroxylamines (II), whose structure was determined unequivocally by x-ray structural analysis. The mechanism of solvolysis of triazolines (I) is discussed, along with the structural characteristics and stabilization factors of the O-tosylhydroxylamine products (II).

Asymmetric nitrogen. Communication 53. Stereochemical characteristics and absolute configuration of the (−)-ℓ-ephedrine salt of 1,6-diazabicyclo[3.l.o]hexane-5-carboxylic acid

Conclusions1.We established the N(S)N(S)C(R) configuration of levorotatory derivatives of 1,6-diazabicyclo [3.1.0] hexane-5-carboxylic acid.2.Steric and electronic factors (repulsion of atoms, n- σ interaction, repulsion of unshared electron pairs, and also the unshared pair-vicinal bond) are apparent in the conformation and in the general geometry of diazabicyclo [3.1.0] hexanes.

Asymmetrical nitrogen. 51. Synthesis and optical activation of 1,6-diazabicyclo-[3.1.0]hexane-5-carboxylic acid and its derivatives

Conclusions1.Total separation of the (−)-1S,5R,6S- and (+)-1R,5S,6R-enantiomers of the stable l,6-diazabicyclo[3.1.0]hexane-5-carboxylic acid is effected via the diastereoisomeric salts with l-ephedrine.2.The diastereoisomeric α-phenylethylamides of l,6-diazabicyclo[3.1.0]hexane-5-carboxylic acid have been obtained in relatively low optical purity (10–12%) by amidating the methyl esters followed by recrystallization and the asymmetric epimination of Δ1-pyrroline-2-carboxylic acid S-α-phenylethylamide.

Asymmetrical nitrogen. Communication 34. Steric selectivity of the methylenation of activated O-alkyloximes

Conclusions1.The synthesis of 1-alkoxyaziridines under the control of a chiral O-substituent by the reaction of O-alkyloximes with dimethylsulfonium methylide or the acid decomposition of 1-alkoxy-2,2-bis(trifluoromethyl)-Δ2-1,2,3-triazolines proceeds stereoselectively with the predominant formation of the thermodynamically favored diastereomers.2.The intermediate formation of kinetically and thermally unstable Δ2-1,2,3-triazolines was confirmed in the reaction of O-alkylisonitrosomalonates with diazoalkanes.3.A scheme was proposed for the trans-stereoselective methylene insertion into the C-C bond of O-alkylisonitrosomalonates leading to the formation of Z-O-alkylisonitrososuccinates.