Cyclische Nitrone, III. Konfigurationsbestimmungen an Aldonitronen mit Hilfe von UV‐Spektren

Dedicated to Professor Dr. A . Eschenmoser on the occasion of his 60th birthday (6.V1.85)The hypothesis which explains the diastereoselectivity of the 1,3-dipolar cycloaddition of the N-glycosylnitrones 1-3 leading to the 5,s-disubstituted isoxazolidines 4 6 on the basis of a kinetic anomeric effect predicts that nucleophiles should add to N-glycosylnitrones with a high degree of diastereoselectivity. To test this prediction, the nucleophilic addition of lithium and potassium dialkylphosphites to the crystalline (Z)-nitrone 11, prepared from oxime 9 and (benzy1oxy)acetaldehyde has been examined. The addition of lithium phosphites gave the N-glycosyl-N-hydroxyaminophosphonates 12-16 (d. e. 78-92%) in high yields (Scheme 4). The addition of potassium phosphites showed a much lower diastereoselectivity. Glycoside cleavage, hydrogenolysis, and dealkylation of 12-16 gave (+)-(S)-phosphoserine (+)-19 (34-45 % from 9).Its absolute configuration was confirmed by an X-ray analysis of the N-(3,3,3-trifluoro-2-methoxy-2-phenylpropionyl) derivative 24. Similarly, the crystalline nitrone 25 gave the N-glycosyl-N-hydroxyaminophosphonate 26, which was transformed into ( +)-(S)-phosphovaline (+)-31 (42% from 9). The diastereoselectivity of the nucleophilic addition and the enantiomeric purity of ( + )-31 were determined by the analysis of the derivative 30 (d.e. 92%) and 32 (d.e. 93%), respectively. The addition of lithium diethyl phosphite to the nitrone 33, prepared in situ, gave the N-glycosyl-N-hydroxyaminophosphonate 34 (41 %;d.e. 91 YO), which was transformed in (+)-(S)-phosphoalanine (+)-37 (21 Sb from 9).

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“…J(H,,P) expected for conformer G [29] is [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Hz.…”

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confidence: 99%

Nucleophilic Additions to N‐Glycosylnitrones. Asymmetric Synthesis of α‐Aminophosphonic Acids

Huber¹,

Knierzinger²,

Obrecht³

et al. 1985

Helvetica Chimica Acta

105

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“…Alternatively, the hydroxylamine (X) could be directly converted into the pyrroline (XII) by melting it with potassium hydrogen sulfate. I t may be noted that the ultraviolet spectrum of X I shows absorption a t somewhat lower wavelength and intensity than that of 2-phenyl-1-pyrroline-1-oxide (12). This is attributed to a certain degree of steric inhibition of conjugation analogous to that which has been observed with a series of phenyl ketones (13 For personal use only.…”

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confidence: 90%

Studies in the Pyrroline Series: V. 3,3-Dimethyl-1-Pyrroline-1-Oxide

Bonnett¹,

Ho²,

Raleigh³

1965

Can. J. Chem.

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The pyrolysis of 1-ethyl-3,3-dimethylpyrrolidine-1-oxide gives 1-hydroxy-3,3-dimethylpyrrolidine, which, on dehydrogenation, 3,3-dimethyl-1-pyrroline-1-oxide. The identification of the nitrone is described. The cyclo-additions of styrene to this nitrone and t o 5,5-dimethyl-1-pyrroline-1-oxide were investigated, and the direction of addition was deduced from the n.m.r. spectra of the adducts.In connection with other work (1) it was desired to prepare pyrroline ring systems v ith geminal substitution a t a p-position, and to this end attenlpts were made to syntliesize one or more of the di~nethyl compounds I-IV.Three approaches were tried. The first followed the nitroalkane synthesis (2) and involved the attempted conjugate addition of nitromethane to senecialdehyde, this being the first step on the route to I1 and IV. Under a variety of reaction conditions, no absorption due to an unconjugated carbonyl group was found in the infrared spectrum of the product, and it was concluded that 1,4-addition had not occurred to an appreciable extent. This result is presumably due to the steric effect of the substituents a t the pposition of the unsaturated aldehyde, and it is pertinent that, whereas nitronlethane adds readily across the conjugated system of acrolein (3), in the reactioil of crotonaldehyde with nitroinethane, conjugate addition is not the main path.The second approach, which suffered from the disadvantage that it would be expected to yield a mixture of isomers 111 and IV, was the direct oxidation of the corresponding secondary ainine to the cyclic hydroxylamine (ref. 4, cf. 5 ) followed by dehydrogenation to the nitrone.As others have recently reported (6, 7), some difficulty was experienced with the direct oxidation with hydrogen peroxide, a step which gave erratic and low yields. The best yield 'For Par1 I V see R. Bonnell. J. Cltem. SOG. 2313 (1966.

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“…The hydrogenation occurs as for isoxazoline N-oxides 141. The kinetics of the isomerization (1) -f (2) was studied in several solvents by measuring the decrease in extinction of the UV band of (I) at 345 nm. In all cases, the reaction was clearly of the first order.…”

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“…The velocity increases with increasing polarity of the solvent; half-reaction times are 140 h in nhexane, 70 h in diethyl ether, 2 h in ethanol. Solid ( I ) isomerizes to (2) within several weeks. The unusua1 cyclization must be due to the strong steric hindrance by the four substituents around the C=C bond.…”

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Electrolytic Desulfurization of 2‐Mercapto Carboxylic Acids and the Corresponding Disulfides

Rambacher¹,

Mäke²

1968

Angew. Chem. Int. Ed. Engl.

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Cyclische Nitrone, III. Konfigurationsbestimmungen an Aldonitronen mit Hilfe von UV‐Spektren

Cited by 16 publications

References 3 publications

Nucleophilic Additions to N‐Glycosylnitrones. Asymmetric Synthesis of α‐Aminophosphonic Acids

Nucleophilic Additions to N‐Glycosylnitrones. Asymmetric Synthesis of α‐Aminophosphonic Acids

Studies in the Pyrroline Series: V. 3,3-Dimethyl-1-Pyrroline-1-Oxide

Electrolytic Desulfurization of 2‐Mercapto Carboxylic Acids and the Corresponding Disulfides

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