Clarke, Thomas Carl (1974) I. Investigations on the mechanism of thermal decomposition of 1-pyrazolines. II. The stereochemistry of solvolytic displacement and intramolecular nucleophilic substitution by a double bond at a vinyl center. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-10142005-153023
I. Two mechanisms have been proposed to account for the net single inversion of stereochemistry observed in the pyrolysis of 3,5-dialkyl-1-pyrazolines. The first, involving initial cleavage of both C-N bonds and formation of a [pi]-cyclopropane intermediate, predicts completely racemic singly inverted product on pyrolysis of an optically active pyrazoline. The sequential C-N bond cleavage proposed in the second mechanism predicts that, to the extent that the rates of initial cleavage of the two ON bonds are different, some optical activity should be observed in the singly inverted product. In order to resolve this problem, the pyrolysis of (+)-(3R,5R)-trans-3-ethyl-5-methyl-1-pyrazoline was undertaken. Flow pyrolysis of this pyrazoline at 292° and atmospheric pressure led to 71% cis-1-ethyl-2-methylcyclopropane, 27% trans-1-ethyl-2-methylcyclopropane and minor amounts of olefin product. The cis cyclopropane was formed with 0.8% retention of optical purity while the trans product showed 23% retention of optically purity. Correlation of these results with the pyrolyses of this pyrazoline specifically deuterated at C3 and C5 will allow a distinction between the two mechanistic possibilities. This work is currently in progress.
II. In order to determine the stereochemistry of solvolytic displacement and intramolecular nucleophilic substitution by a remote double bond at a vinyl center, the synthesis and solvolysis in trifluoroethanol of (Z)- and (E)-3-methyl-2,6-heptadien-2-yl trifluoro-methanesulfonate were undertaken. In addition to 3-methyl-1,2,6-heptatriene and the products of solvolytic displacement, four cyclized trifluoroethyl ether products were formed. These four products were also generated in the trifluoroethanolysis of 1,2-dimethyl-1-cyclohexen-4-yl tosylate. Net inversion of stereochemistry was observed in both the solvolytic displacement and cyclization processes in the vinyl triflates. Solvolysis of (Z)- and (E)-3-methyl-2-hepten-2-yl trifluoro-methanesulfonate also resulted in net single inversion in the vinyl trifluoroethyl ether products. These results are explained in terms of competitive attack on the initially formed ion pairs and on free vinyl cation intermediates.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Chemistry and Chemical Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||20 December 1973|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||14 Oct 2005|
|Last Modified:||26 Dec 2012 03:05|
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