I. (+)-3R,5R- and (+)-3R,5S-3-ethyl-5-methyl-1-pyrazolines
(34T and 34C, respectively) have been prepared in optically active
form. Their stereochemistries have been determined by correlation
with (-)-R-3-hexanol and (-)-R-2-bromohexane. Pyrolysis of these
pyrazolines in the gas phase at 292° allows a complete study of the
stereochemistry of the 1-pyrazoline decomposition. 34T yields
cis-1-ethyl-2-methylcyclopropane (48C) in nearly racemic form and
trans-1-ethyl-2-methylcyclopropane (48T) 22.5% optically active
with predominant inversion of the alkyl groups. 34C yields cis-
1-ethyl-2-methylcyclopropane (48C) 36.5% optically active with
predominant retention of stereochemistry and trans-1-ethyl-2-methycyclopropane
(48T) 14.2% optically active with predominant single
inversion of the ethyl group.
II. A series of phenyl-substituted 2H-azirines: 3,3-dimethyl-
2-phenyl-2H-azirine (33c), 3-methyl-2-phenyl-2H-azirine (33a),
3-ethyl-2-phenyl-2H-azirine (33b), and 2,3-dimethyl-3-phenyl-2H-azirine
(33d) were synthesized and their thermal decompositions
were investigated. 2-aza-1,3-butadienes were formed as primary
pyrolysis products from 33a-c, which indicates that the thermal
reaction proceeds via carbon-carbon bond cleavage leading to iminocarbene
intermediates. 33d yields 2,3-dimethylindole as its only
pyrolysis product, which indicates initial carbon-nitrogen bond
cleavage leading to vinyl nitrene: intermediates. Further thermal
reactions of the azabutaaienes to yield olefins and nitriles, and
dihydroisoquinolines were also studied.