Stereochemical studies. VIII. Asymmetric selection via elimination. Assignment of nitrogen chirality by pyrolytic elimination in optically active amine oxides

Abstract

ethylene glycol, 6.9 g of the mixture of 25 and 27, and 6.0 g of hydrazine hydrate, at 210" for 3 hr. The mixture was diluted with water, neutralized, and extracted three times with ether to give 1.7 g (about 30% yield) of an oil, bp 110-1 12" (2 mm). Gas chromatography on column A (see above) separated, with difficulty, (-)-2-methyl-2-ethylpentanoic acid (26) from its isomer 28, 3-methyI-3-ethylpentanoic acid. The ir spectrum of 26 was identical with that of authentic material, made after Prout.16 The mixture of 26 and 28 was used in the next step, in which 1.4 g of the mixture (0.01 mol) was treated with 3 ml of thionyl chloride at room temperature for 18 hr. After heating to reflux for 2 hr, the thionyl chloride was removed in uacuo, 0.5 g of activated sodium azide and 3 ml of xylene were added, the solution was heated to 80", and another 0.5 g of sodium azide was added. After 5 hr, the temperature was raised to 180". The filtrate was stirred for 12 hr with 4 ml of concentrated hydrochloric acid at about 80" and cooled, the aqueous layer separated, and the organic solution extracted once with hydrochloric acid. From the aqueous layers, the amine was liberated by Stereochemical Studies.Abstract: The four possible optically active stereoisomeric N-methyl-N-neopentyl-4-methylcyclohexylamine oxides were individually prepared. The stereomeric secondary amines, cis-and trans-N-neopentyl-4-methylcyclohexylamines (3 and 4), obtained by reductive amination procedures, were separated and converted to the corre-

Novel Oxygen Chirality Induced by Asymmetric Coordination of an Ether Oxygen Atom to a Metal Center in a Series of Sugar-Pendant Dipicolylamine Copper(II) Complexes

“…It is well-known that a nitrogen lone pair inverts via pyramidal inversion, , causing expeditious loss of chirality at a stereogenic nitrogen center. Thus, asymmetric nitrogen atoms that have been characterized have been limited to a series of quaternary ammonium ions , and N -oxides, , protonated , or metal-coordinated − amine ligands, and free tertiary amines with adequate electronic and structural , restrictions. Among them, asymmetric nitrogen atoms coordinated to metal centers are of particular interest as the chirality exists in the primary coordination sphere of the metal ion, potentially influencing the physical and chemical properties of the metal center .…”

Enantioselective Photochemical Synthesis of a Simple Alkene via the Solid State Ionic Chiral Auxiliary Approach

“…The preparation of enantiomerically pure simple (unfunctionalized) olefins is difficult because their resolution through direct Pasteur techniques is essentially impossible . Several approaches have been taken to the asymmetric synthesis of simple chiral olefins: (1) asymmetric Wittig-type reactions with chiral cyclic phosphonamides, (2) asymmetric elimination reactions of N -chiral amine oxides, (3) asymmetric Hoffman elimination of N -chiral quaternary ammonium salts, and (4) asymmetric radical fragmentation reactions of S -chiral sulfoxides . For the most part, the thermal solution phase 1,2-elimination reactions mentioned above give low ee values.…”

Photoisomerization of certain stilbenes to 9,10-dihydrophenanthrenes

“…We have re-solved4 oxides 1 and 2 and determined their senses5 and magnitudes6 of nonequivalence in chiral 3 and several related chiral alcohols. In optically pure (S)-(+)-3, the C-methyl and A-methylene groups of (-)-enriched 1 show high-field senses of nonequivalence (0.019 and 0.017 ppm, respectively) whereas the A-methyl group shows low-field nonequivalence of 0.029 ppm. For (-)-enriched 2, the senses of nonequivalence are the same, but the respective amounts of nonequivalence are 0.028, 0.005, and 0.019 ppm.…”