An investigation of the cycloaddition behavior of dichloroketene with various types of olefins seemed in order to determine if dichloroketene behaved similarly to dialkylketenes. It was anticipated that a study of this type would indicate the reactivity of dichloroketene to various types of olefinic compounds and thus establish if the ease of cycloaddition with dichloroketene parallels the nucleophilicity of the olefin as it does in dialkylketenes.

This dissertation is a study involving the synthesis and chemistry of arylhaloketenes and cyclopentadiene cycloadducts, and a study of the cycloadduct isomer distribution was begun.

It was proposed to study the cycloaddition of ketenes and carbodiimides in some detail. The first objective was to investigate the general applicability of the reaction as a tool for the synthetic organic chemist in the preparation of a new class of substituted β-lactams; i.e., imino-β-lactams. It was proposed for this part of the research problem to look for the intermediate, either directly or indirectly, by trapping experiments. It was further proposed to study substituent effects in the ketene and carbodiimide and also Investigate the effect of solvent polarity on the reaction rate. From these data, it was hoped that the mechanism of the cycloaddition reaction could be elucidated.

The research described within this thesis may be divided into four main subject areas: 1) The use of (Z)-2H-heptafluorobut-2-ene (10) as a synthon for hexafluorobut- 2-yne (4) in Diels-Alder reactions was investigated. Novel 'one-pot' routes to a variety of bis(trifluoromethyl) substituted furan and arene derivatives were discovered, along with the synthesis of the novel diene, bis(trifluoromethyl)cyclopentadiene (46), from cyclopentadiene.2) A variety of nucleophiles were successfully reacted with (10), the products of which were identical to those that have been, or would be expected to be, formed from the reaction of the same nucleophile with (4). A novel route to a fluorinated quinoline derivative was also discovered.3) Perfluoroperhydrophenanthrene (74) was used as a 'bulking agent' to replace the hydrocarbon solvent used in halogen exchange reactions for the preparation of octafluorocyclopentene (3), chlorofluoro -pyridine, -pyrimidine, and -benzene derivatives. New 'one-pot' syntheses of hexafluorobut-2-yne (4), octafluorobut-2-ene (6) and hexafluorocyclobutene (2) were also discovered.4) Various routes were explored in an attempt to improve the present literature preparations of tetrafluoropropyne (79), including pyrolysis and elimination methods. Tetrafluoroallene (81), and trace amounts of (79), were found to be formed on the elimination of hydrogen fluoride from 2H-pentafluoropropene (5).

A comprehensive investigation of cycloalkenyl-alkyne coupling reactions mediated by cobalt(III) templates is presented. The in situ derived cationic 3-cyclohexenyl complexes of cobalt(III) react with some terminal alkynes to afford either 1,4-bicyclo[4.3.1]decadienyl or 2,3-vinylcyclohexenyl products, depending on the type and concentration of the alkyne. The mechanism for this cyclohexenyl-alkyne cycloaddition reaction is consistent with the previously reported cobalt-mediated [3 + 2 + 2] allyl-alkyne coupling reaction. The carbon-carbon bond activation/cyclopentenyl-alkyne ring expansion process was also studied using the 1,3-di-tert-butylcyclopentadienyl cobalt system. A modified synthetic strategy to the requisite half-sandwich cobalt(I) cyclopentadiene precursor was developed using cobalt(II) acetoacetonate, avoiding the use of simple cobalt(II) halides which are prone to ligand disproportionation. Furthermore, the preparation of the cobalt(III) cyclopentenyl precursor, (t-Bu2C5H3)Co(4-C5H6), was accomplished via hydride addition to the easily prepared cobalticenium complex [(t-Bu2C5H3)Co(C5H5)]BF4 and avoids the use of the thermally sensitive (t-Bu2C5H3)Co(ethylene)2. Disubstituted alkynes such as 2-butyne or diphenylacetylene undergo cyclopentenyl coupling to afford the corresponding 5-cycloheptadienyl products, albeit in lower yields compared to the pentamethylcyclopentadienyl cobalt system. The 1,3-di-tert-butylcyclopentadienyl ancillary ligand shows unique and unusual reactivity, coupling with tert-butylacetylene to afford a novel spiro[4.5]decatrienyl complex. Ultimately, the poor isolated yields of seven-membered products demonstrate that the disubstituted cyclopentadienyl ligand system is a poor candidate for future studies in this area. A mechanistic investigation of the cobalt-mediated carbon-carbon bond activation process was performed. Cationic cobalt 2-vinyl complexes were proposed as viable intermediates in the activation process and synthetic routes to these compounds were examined. However, the resulting vinyl complexes were unstable and could not be directly isolated and characterized. Preparation of cobalt vinyl complexes in the presence of cycloalkadienes did not furnish the expected cycloexpanded products, suggesting alternative routes to the cobalt vinyl intermediates are necessary. During the course of the mechanistic investigation, a high-yielding alternative synthetic procedure for (C5Me5)Co(4-butadiene) from the easily prepared precursor, [(C5Me5)CoI2]n, was found, circumventing the use of the thermally sensitive (C5Me5)Co(ethylene)2.

No description available.

No description available.

No description available.

Konstanz, Univ., Diss., 2007.

University, Diss., 2005--Würzburg. / Dateien im PDF-Format.