published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.

No description available.

No description available.

The reactions of 2,5-dimethoxytetrahydrofuran and 2,6-dimethoxytetrahydropyran with halotrimethylsilanes have unexpectedly given 1,4-dichloro-1,4-dimethoxybutane and 1,5-dihalo-1,5-dimethoxypentane, respectively. Some features of this reaction were investigated and a mechanism was proposed. / It was shown that 1,4-dichloro-1,4-dimethoxybutane was a mild reagent for the conversion of primary amine and amide to the corresponding N-alkyl and N-acyl pyrroles, respectively. As part of these applications, 2-(2-formylpyrrol-1-yl)-4-methylpentanoic acid, a compound isolated from flue-cured tobacco, was synthesized. / The use of acylpyrroles as active acylating agents was investigated. The preparation of (alpha)-substituted derivatives from ethyl 2-(1-pyrrolyl)acetate was achieved by using lithium hexamethyldisilazide as base. / As part of a synthetic study directed toward Nonactin, the bicyclic enol form 152 and keto form 153 were obtained by the reaction of 1-methoxyl-1,3-bis(Trimethylsiloxy)-1,3-pentadiene with 2,5-dimethoxytetrahydrofuran. The configurations at C-4 were determined with the aid of 200 MHz ('1)H nmr decoupled spectra. / A new rearrangement of (alpha)-acyloxy esters into 2-hydroxy-3-keto esters was observed.

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This thesis is concerned with studies towards the total synthesis of a class of natural products - the oxazolomycins. Attention was focused on the left-hand side triene fragment and right-hand side lactam heterocyclic system. This thesis describes the synthesis of a racemic terminal phenyl analogue of oxazolomycin A and C, possessing the left-hand side triene geometry as required. A novel truncated pyridine analogue is also described. The molecules represent a racemic total synthesis of analogues of phthoxazolin A and inthomycins B and C. The synthesis is based upon a crucial Stille cross-coupling reaction between stannane and diene iodide fragments. The stannane fragment was synthesised using literature precedented methods and the vinyl halide prepared using a highly stereoselective Wittig, Takai homologation or Stork reaction leading to a variety of ratios of mixtures of Z, E and E, E diene halides. These investigations led to the availability of 1:1, 3:1 and 1:3 mixtures of Z, Z, E : Z, E, E left hand side triene fragments possessing the required stereochemistries for oxazolomycin A and C. Utilising existing methodology developed in the Moloney group, investigations were carried out towards construction of β-keto esters possessing terminal hydroxyl functions, suitable for diastereoselective aldol ring closure. Following extensive protecting group manipulation and N-acylation coupling optimisation, a TIPS protected β-keto acid, existing as predominantly the keto tautomer, was successfully coupled to an oxazolidine heterocycle. This N-acylated oxazolidine upon Dieckmann cyclisation would present an advanced intermediate of opposite configuration (Lserine is used here as a cheaper starting material for the construction of the oxazolidine instead of D-serine) to the oxazolomycin right-hand side.

An alternate approach to the synthesis of calix[3]indoles has been demonstrated, but further attempted synthetic approaches to calixindoles using new leaving groups led to uncharacterized polymeric products. The synthesis of new 7,7'-diindolylmethane- 2,2'-dicarbaldehydes gives potential for further ligand design and metal complex formation. In addition, 4,6-dimethoxyindole-7- carbaldehydes have been effectively converted to a range of 6-methoxyindole-4,7-diones by Dakin oxidation. Various electrophilic substitution reactions have been performed on the 4,6-dimethoxybenzimidazoles. Formylation, acylation, acid catalyzed addition of formaldehyde and nitration revealed that the activated benzimidazoles are less reactive at the specified C-7 position compared to the analogous indoles. The key starting material for a potential calixbenzimidazole was synthesized by the selenium dioxide oxidation of 2-methyl-7-formyl-4,6-dimethoxybenzimidazole and by oxidative cleavage of 4,6-dimethoxy- 2-styrylbenzimidazole by Lemieux-Johnson reagent followed by reduction. Nevertheless, attempted preparation of calixbenzimidazole from 2-hydroxymethyl-4,6-dimethoxy benzimidazole led to formation of a dibenzimidazolyl ether. The synthesis of some novel activated bisbenzimidazoles has been developed. Furthermore, benzimidazoles were incorporated into new ligand systems which have led to a wide range of acyclic quadridentate neutral metal complexes. Activated benzimidazoles overall illustrate one electron irreversible oxidation to form a radical cation followed by multielectron oxidations. On the other hand, the nickelII and cobaltII benzimidazole metal complexes investigated showed one electron ligand centered reversible reduction. Irreversible radical cation oxidation followed by multielectron oxidation of the metal complexes further demonstrates the rich electrochemical nature of the 4,6-dimethoxybenzimidazoles. Some novel 7-(indol-2-yl)-4,6-dimethoxybenzimidazoles were prepared with indolin-2-one and triflic anhydride and an alternate procedure afforded 2-(4,6-dimethoxyindol-7-yl)-benzimidazoles from activated indoles and 2-benzimidazolinone. Two new isomeric series of 2-substituted-5,7-dimethoxybenzothiazoles and 2-substituted-4,6-dimethoxybenzothiazoles were synthesized via Jacobson cyclization. The two strategically placed electron donating methoxy groups activate these benzothiazoles to undergo various electrophilic substitutions at the 4- and 7- positions respectively.