An attempt to obtain chiral induction across the carbamate linkage (-NCOO-), using chiral amines and the benzyl carbamate, was embarked upon. Initial studies centred around the benzyl carbamate protected form of a,a-diphenylpyrrolidinemethanol. The inability to protect the alcohol in this compound led to further investigations into differently structured molecules, these being 2-(1-phenylcyc1opentyl)-4,4,6-trimethyltetrahydro-l,3-oxazine and N-biphenyl benzyl carbamate. Chiral induction was not achieved, but the investigations therein led to two new fields of study. A trans-carbamation type cyclisation reaction was found to occur in the a,a-diphenyl-(2pyrrolidine- N-benzyl carbamate)methanol compound yielding the bicyclic 2-oxazolidone, 3-oxa-l-aza-4,4-diphenylbicyclo[3.3.0]octan-2-one, with nitrogen at the bridgehead position. Sodium hydride was the base used to facilitate this reaction. Further studies into this reaction and this class of compounds were inconclusive. The second field of study was the initial investigation into novel N-monosubstituted carbamate rearrangement reactions to yield a substituted alcohol, of the benzyl alcohol type. The rearrangement occurs when the carbamate is treated with butyllithium at O°C and the reaction allowed to warm to room temperature. The rearrangement was shown to occur when the substituent on the nitrogen is aromatic in nature, this group being able to contain a hetero-atom and be substituted. A positive result was also obtained when the 0-carbamate moiety was the benzyl or cinnamyl group and to a much lesser degree the allyl group. The products obtained from the rearrangement of the benzyl carbamates were a-aryl- a-phenylmethanols (substituted benzyl alcohols / benzhydrols), with the analogous product, l-aryl-3-phenylprop-2-en-l-ol, being obtained from the cinnamyl alcohol. A benzylic substituted benzyl carbamate rearranged to give the tertiary alcohol. It was found that the rearrangement occurred to the position on the aryl substituent to which the nitrogen had been attached. From the results obtained no conclusive mechanistic details could be determined, but it was proposed that the reaction intermediate contained a five-membered cyclic structure. It is assumed that the rearrangement occurs with concomitant loss of cyanic acid (HNCO). / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

The carbamate functionality has always been associated with a major class of biocides because of its ability to function as an inhibitor of the enzyme acetylcholinetransferase. However, carbamates are not limited to pesticidal applications, they have also shown potential as intermediates in organic synthesis. Research has shown that amongst its other properties, the carbamate group has the ability to migrate, function as a leaving group and participate in rearrangement reactions. As part of ongoing research at this department on the synthetic utility of the carbamate group, this project has been primarily concerned with the chemistry of carbamates in conjunction with thiophene, an aromatic heterocycle. The thiophenes also represent an important class of organic compounds. They are found in natural products, biologically and pharmacologically active systems (both naturally occurring and synthetic), synthetic precursors and more recently, organic conductors and electro-optical devices. In exploring the chemistry of thiophene carbamates, the unique nature of the thiophene ring has been shown to affect the synthesis and reactions of these compounds; the often peculiar character of thiophene imparts properties which make these carbamates remarkable and distinct from carbamates of other aromatic and conjugated systems such as benzene and conjugated polyenes. With a wide range of potential applications, the purpose of this project has been to study the synthesis and reactions of thiophene carbamates, in particular, the reaction of deprotonated thenyl carbamates with electrophiles, using the electrophile as a means of studying the charge delocalisation in such systems. A series of thenyl carbamates has been synthesised from thenyl alcohols and their reactions with electrophiles have been studied. The electrophilic substitution reactions illustrate the possibilities for the functionalisation of these compounds, particularly remote functionalisation via anionic charge migration; the charge has been found to migrate across five carbon atoms, a phenomenon not observed in this department's studies of other carbamate systems. The substitution products which form in these reactions depend on the nature of both the carbamate and the electrophile. In addition, three rearrangements (carbamate to amine, substituted carbamate to alkene, and substituted carbamate to a-hydroxyamide) have been observed which may find application in organic synthesis. The potential uses for these carbamates range from biologically active applications as carbamates or as derivatives (amines or alkenes via rearrangement or alcohols via deprotection); many contain a chiral centre and thus may be used in enantioselective or diastereoselective processes in the synthesis of other products, as well as the industrial applications in the fields of non-linear optics and conducting polymers. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

Carbamate chemistry has flourished since the 1980's which saw the introduction of the carbamoyl group by Hoppe and co-workers, prominent researchers in this area, as a suitable moiety for the activation and stabilisation of alpha-heterocarbanions which are important intermediates in synthetic organic chemistry. This functionality increases a-CH acidity and stabilises the a-lithiocarbanion thus generated. The versatility of the carbamate group has spawned investigations into the numerous possibilities that exist for the functionalisation of the carbon alpha to the carbamate group. Some of these possibilities were explored in the present work. The direct formation of stable benzylic carbanions alpha to an oxygen atom is not a facile process as such lithiated species are unstable and readily undergo a 1,2-Wittig rearrangement. However, protection of the alcohol as the carbamate enabled functionalisation of both benzylic sites with a variety of electrophiles. Benzyl carbamates were found to react regioselectively with a,~-unsaturated electrophiles to afford either the 1,2- or l,4-addition products. The regioselectivity could be controlled by the presence or absence of a silyl moiety, either a trimethylsilyl or tertbutyldimethylsilyl moiety, attached at the benzylic position, alpha to the carbamate. The reaction of benzyl carbamates with 2-cyclohexen-1-one and 2-butenolide afforded the 1,2-addition adducts in moderate to good yields (25-66%). The isolation of the masked ahydroxy ketone resulting from the opening of the lactone ring on reaction of 2-butenolide with benzyl N,N-diisopropylcarbamate was surprising, as this electrophile is known to behave as an excellent Michael acceptor. The introduction of a silyl moiety at the benzylic position facilitated conjugate addition, yielding the corresponding Michael addition products. A novel cyclisation was observed on reaction of a-silyl benzyl carbamates with methyl acrylate to give the a,y;y-trisubstituted butanolides (y-butyrolactones). The proposed vii mechanism of this reaction is discussed and illustrates the migrational ability of the carbamate functionality. Chiral induction in benzylic systems has only been investigated by a few authors. In the present investigation two possible routes to chiral induction at the benzylic position were investigated using either a (-)-sparteine-mediated transformation or chiral carbamates derived from (L)-proline. (-)-Sparteine mediated transformations were solvent dependent with the best enantiomeric excess of 28% being obtained. The results indicated that racemisation at the benzylic position was faster than reaction with an electrophile. The chiral carbamates were only slightly more successful yielding the a-substituted adducts with diastereoselectiVities of the order of 20-50%. The diastereoselectivities were found to be enhanced by the addition of HMPA which coordinated with the transition state blocking one of the faces to attack by the electrophile. The 1A-addition reaction with 2-butenolide was particulary useful as it allowed the exploration of the synthesis of lignan derivatives from benzyl carbamates. Lignans are secondary plant metabolites and exhibit.a wide range of biological activities. Applying the methodology developed to the synthesis of lignans resulted in the preparation of an arylnaphthalene lignan, in 79%, and the partial synthesis of racemic fargesin, a racemic furofuran lignan. This natural product synthesis highlighted the difficulty in removing the carbamate functionality and re-introducing the alcohol moiety. Thus, hydrolytic cleavage of the benzyl carbamates was investigated using a selection of mineral acids. Depending on the reaction conditions, the products were found to be the corresponding benzyl alkanoates or benzylhalides. The alkanoates are derived from nucleophilic displacement of the initially formed benzyl halide A novel deprotection of a-silyl benzyl carbamates was also observed in which the carbamoyl group was cleaved to afford the a-silyl alkanoates and chlorides without the loss of the silicon moiety. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1997.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1961. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thèse (M.Sc.) -- Université Laval, 1997. / Bibliogr.: f. [82]-88. Publ. aussi en version électronique.

This thesis has been divided into three main sections. The first chapter contains a review of the total synthesis of lactacystin and also its derivatives. Chapter two consists of our own synthetic work, and experimental details are provided in chapter three.

Reproduction de : Thèse de doctorat : Chimie organique et macromoléculaire : Lille 1 : 2006. / N° d'ordre (Lille 1) : 3881. Texte en français et en anglais (partie expérimentale). Résumé en français et en anglais. Titre provenant de la page de titre du document numérisé. Bibliogr. à la suite de chaque chapitre.

Thesis (Ph. D.)--University of Washington. / Bibliography: l. [87]-89.

Th. 3e cycle--Molécules de synthèse à propr. pesticides ou thérapeutiques--Toulouse--I.N.P., 1979. N°: 55.

Call number: LD2668 .T4 1978 P35 / Master of Science