Part I. Mechanism of the Thermal Isomerization of 2-Norbomene-5,6-Endodicarboxylic Anhydride. Part II. The Aldoketene Dimer Rearrangement

Author: Baldwin, John Edwin

Year: 1963

Degree: Dissertation (Ph.D.)

Advisor: Roberts, John D.

Committee Member: Unknown, Unknown

Option: Chemistry; Physics

DOI: 10.7907/83K8-TP73

Abstract

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PART I

The Diels-Alder adduct of cyclopentadiene and maleic anhydride, 2-norbornene-5,6-endo-dicarboxylic anhydride, may be rearranged thermally to its exo-isomer. This isomerization is known to occur in part through an internal mechanistic pathway. In order to study the mechanism of this rearrangement, an attempt was made to synthesize 2-norbornene-5,6-endo-dicarboxylic anhydride stereospecifically labeled with carbon-14 in one carboxyl group, rearrange this material under conditions favoring the internal pathway, and degrade the exo-anhydride in a stereospecific fashion, measuring the carbon-14 activities of each carbonyl group separately.

Three synthetic approaches to the stereo specifically labeled endo-anhydride, through the intermediates ethyl cis-[...]-cyanoacrylate, (-)-menthyl hydrogen maleate, and (-)-menthoxymalealdehydic acid, have not been successful. Rearrangement of the endo-anhydride in the presence of tetracyanoethylene gave exo-anhydride from the internal mechanism and 2,2,3,3-tetracyanonorborn-5-ene from the external process. Degradation of 2-norbornene-5,6-exo-dicarboxylic anhydride by hydrogenation and reaction with (-)-menthol gave two diasteromeric (-)-menthyl hydrogen 2,3-exo-norbornanedicarboxylates, whose absolute configurations were established by degradation of one to an optically active 2-exo-norbornanecarboxylic acid.

2,3-Endo-norbornanedicarboxylic anhydride was rearranged to its exo-isomer when heated to 250º for 18 hours.

PART II

The neutral phenylketene dimer has been synthesized, identified as 3-hydroxy-2,4-diphenyl-3-butenoic lactone, reduced to [...],[...]-diphenylbutyric acid, and rearranged with base to an acidic isomer, tentatively postulated to be 2,4-diphenylcyclobutanedione or 2,4-diphenylcyclobutenolone.

Structural assignments for neutral methylketene dimer, acidic methylketene dimer, 3,5-dimethyl-6-ethylpyronone, 3,5-diphenyl-4-hydroxy-6-benzylpyrone, and 3,5-dimethyl-4-hydroxy-6-ethylpyrone have been confirmed or corrected.

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