STEREOCHEMICAL STUDIES .8. ASYMMETRIC SELECTION VIA ELIMINATION . ASSIGNMENT OF NITROGEN CHIRALITY BY PYROLYTIC ELIMINATION IN OPTICALLY ACTIVE AMINE OXIDES

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-methylcyclo-hexylamines (3 and 4), obtained by reductive amination procedures, were separated and converted to the corresponding tertiary amines (8 and 9) by N-methylation. The cis- and trans-amine oxides (10 and 11) were obtained by oxidation of 8 and 9 with peracetic acid. A consistent correlation of nmr signal envelope shapes at each synthesis stage provided the basis for assignment of stereochemistry to these compounds. Resolution of the amine oxides gave the four optically active stereoisomers in undetermined enantiomeric purity. Each optically active amine oxide underwent asymmetrically selective pyrolytic elimination to optically active 4-methylcyclohexene of known configuration. Thus, the (–)-cis- and (+)-trans-amine oxides each gave (–)-(S) olefin, while the (+)-(R) olefin was the predominant enantio er obtained from pyrolysis of the (+)-cis- and (–)-trans-admne oxides. These results, plus the reasonable assumption that neopentyl is bulkier than methyl, allowed for definition of nitrogen chirality in each of the amine oxides by a transition-state argument. © 1969, American Chemical Society. All rights reserved.