I. The Synthesis, Absolute Configuration, and Stereochemistry of Thermal Decomposition of (+)-3R,5R- and (+)-3R,5S-3-Ethyl-5-Methyl-1-Pyrazoline. II. Mechanistic Investigations of the Thermal Decompositions of 2H-Azirines

Citation

Wendling, Larry Allan (1976) I. The Synthesis, Absolute Configuration, and Stereochemistry of Thermal Decomposition of (+)-3R,5R- and (+)-3R,5S-3-Ethyl-5-Methyl-1-Pyrazoline. II. Mechanistic Investigations of the Thermal Decompositions of 2H-Azirines. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/DFVF-ZS54. https://resolver.caltech.edu/CaltechTHESIS:02242017-100127779

Abstract

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.

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