Five-membered rings are readily prepared by 5-exo-trig radical cyclization. This thesis is concerned with novel methodology for pyrrolidine synthesis. We have synthesised selenium containing radical precursors from aziridines and α-phenylseleno ketones, and cyclized them to 2,4- and 3,4-disubstituted pyrrolidines. A few examples of 5-exo-dig cyclization were also demonstrated. In another study we investigated the capacity of the nitrogen protecting group to direct diastereoselectivity in the formation of 2,4-disubstituted pyrrolidines. The diphenylphosphinoyl protecting group directed cyclization to occur in a highly cis-selective manner. When cyclizations were performed at 17 oC, cis/trans-ratios as high as 24/1 were obtained. In contrast, cyclization of the unprotected pyrrolidine precursor afforded the trans-diastereomer as the major product (cis/trans = 1/3.3 – 1/20). We also examined the use of a hydroxyl auxiliary for controlling diastereoselectivity in radical cyclization. The required selenium containing radical precursors were synthesised from 2-cyanoaziridines by addition of organometallic reagents, reduction of the resulting aziridine ketone, and benzeneselenol ring-opening of the aziridine. Cyclization at 17 oC produced 2,4-disubstituted pyrrolidines substantially enriched in the trans-isomer (cis/trans = 1/9 – 1/12). Novel radical cyclization approaches to thiazolines and pyrrolines were also tried. The thesis also describes attempts to improve the Hassner aziridine synthesis by employing stannous chloride as a functional group tolerant reducing agent.

Optimized methods for the regioselective and stereospecific synthesis of both trisubstituted and tetrasubstituted olefins as single isomers from E-β-chloro-α-iodo-α,β-unsaturated esters have been developed from previous work done in the Ogilvie lab. These optimized methods have led to the synthesis of trans isomeric enediynes that can be photoisomerized to their respective cis isomers and subsequently undergo microwave-assisted Bergman cycloaromatizations. Furthermore, both cis and trans isomeric enediynes that have propargyl ether substituents have been found to be able to undergo photoactivated Bergman cyclizations without the need for an intermolecular hydrogen donor. A mechanism study has confirmed that the Bergman cyclization products that form without the presence of an intermolecular hydrogen donor undergo a series of 1,5-hydrogen shifts as intermediates. A series of optimizations to these reactions were carried out, in part by utilizing electron-donating or electron-withdrawing functional groups to help stabilize the resulting radicals that form on the intermediates, and thus increase the yield of the associated Bergman cyclization products.

Diamidines are a class of compounds that target the minor groove of DNA and have antiparasitic and antimicrobial properties. Their mechanism of action has not been fully elucidated, but may include changes in DNA topology. In this study we have investigated such changes using methods of gel electrophoresis including ligation ladders and cyclization assays. We found that topology changes were sequence dependent. Compounds typically caused non-anomalously migrating ATATA sequences to migrate as if they were bent, while A5 sequences that normally migrated anomalously became less so in the presence of certain diamidines. Select compounds induced changes in cyclization efficiency that were also sequence dependent; DB75 significantly abolished cyclization in A5 containing sequences but enhanced it in sequences containing ATATA sites.

Optimized methods for the regioselective and stereospecific synthesis of both trisubstituted and tetrasubstituted olefins as single isomers from E-β-chloro-α-iodo-α,β-unsaturated esters have been developed from previous work done in the Ogilvie lab. These optimized methods have led to the synthesis of trans isomeric enediynes that can be photoisomerized to their respective cis isomers and subsequently undergo microwave-assisted Bergman cycloaromatizations. Furthermore, both cis and trans isomeric enediynes that have propargyl ether substituents have been found to be able to undergo photoactivated Bergman cyclizations without the need for an intermolecular hydrogen donor. A mechanism study has confirmed that the Bergman cyclization products that form without the presence of an intermolecular hydrogen donor undergo a series of 1,5-hydrogen shifts as intermediates. A series of optimizations to these reactions were carried out, in part by utilizing electron-donating or electron-withdrawing functional groups to help stabilize the resulting radicals that form on the intermediates, and thus increase the yield of the associated Bergman cyclization products.

Las sales de oro se han convertido en uno de los catalizadores por excelencia en una gran variedad de transformaciones orgánicas mediante la activación selectiva de alquinos, alenos y alquenos. Parte del trabajo de esta tesis doctoral se ha centrado en el estudio de la naturaleza carbénica o carbocatiónica de los intermedios de reacción presentes en las cicloisomerizaciones de 1,5-eninos catalizadas por complejos de oro. De esta forma se han desarrollado distintas metodologías de ciclación dando lugar a diferentes productos tricíclicos a partir de oxo-1,5-eninos o 1,5-bencileninos. Además, se ha podido aplicar estas nuevas metodologías de ciclación en la síntesis de productos naturales como etapa clave de la misma. Por último, nuestro interés se ha centrado en el desarrollo de reacciones intermoleculares de gran utilizad química catalizadas por oro. Por ello hemos desarrollado la síntesis de fenoles substituidos a partir de diferentes acetilenos y furanos. / Gold salts and complexes are the most active catalysts for the activation of alkynes, allenes and alkenes. Part of this Doctoral Thesis is focused on the study of the carbenic or cationic character of the reaction intermediates presents in the cycloisomerizations of 1,5-enynes catalyzed by goldcomplexes. Different methodologies have been developed to synthesize different tryciclic products from oxo-1,5-enynes or 1,5-benzylenynes. Moreover, these methodologies were applied successfully as the key step in the synthesis of natural products. Finally, our interest was focused on the development of intermolecular gold-catalyzed reactions. Therefore, we have developed a general synthesis of trisubstituted phenols from alkynes and furans.

Tetrahydroisoquinoline alkaloids are a class of structurally complex natural products and a huge number of its natural product widely exist in nature which, from the discovery has been more than a century, it compounds with high anti-tumor activity, antibacterial and other physical activity, but also because of its special structure, with low oncentration of biological activity, but these alkaloids are not sold in the market mainly due to a less natural extraction, chemical synthesis method and multi-step, low yield. Therefore, we constructed a combination of tetrahydroisoquinoline alkaloids and the pyrazino [2,1-b] quinazoline-3,6-diones structure of the new compounds, which have the quinazolinone compounds which is the drug synthesis and drug activity on the bond, is also a kind of unique and widely used drug structure, and causes a lot of scientists and drug research interest and discussion, as we develop the motivation.

Pyrazoles have been studied for over a century as an important class of heterocyclic compounds and continue to attract considerable interest due to the broad range of biological activities they possess. The electrophilic cyclization of the acetylenic hydrazones initiated by molecular iodine could provide new ways of synthesizing biologically active 4-iodopyrazole derivatives, which are important precursors for the synthesis of highly substituted pyrazole derivatives. For this reason, we investigated the synthesis of 4-iodopyrazole derivatives, such as 1-aryl- 5-alkyl/aryl-4-iodopyrazoles, starting from phenylhydrazine and ,-acetylenic aldehyde derivatives. Initially, ,-acetylenic aldehydes were synthesized by formylation reaction of corresponding alkynes with DMF. Then, hydrazone derivatives of these aldehydes were prepared by heating them with phenylhydrazine in a neat manner at 55 &deg / C for 5 h. Finally, acetylenic phenyl hydrazone derivatives were subjected to electrophilic cyclization by treating with excess molecular iodine at 80 &deg / C for 3 h. Although electrophilic cyclization is commonly used in organic chemistry, it has not been employed for the cyclization of acetylenic phenyl hydrazones to pyrazole derivatives. Under optimized conditions, these reactions afforded 1-aryl-5-alkyl/aryl-4-iodopyrazole derivatives in moderate to good yields as the single or the major product of the reactions. In some cases, 1-aryl-5-alkyl/arylpyrazole derivatives resulted from these reactions as minor products. In conclusion, 4-iodopyrazole derivatives were synthesized for the first time directly from acyclic starting materials, ,-acetylenic phenylhydrazones and iodine, via electrophilic cyclization.

The one electron oxidant Mn(OAc)3 has been used for years for the oxidative addition of 1,3-dicarbonyls to alkenes to give dihydrofuranes. Since cycloheptatriene is in equilibrium with its valance isomer norcaradiene, it will be interesting to study the reaction of CHT derivatives with Mn(OAc)3 in the presence of 1,3-dicarbonyls. In our research, we have observed that unsubstituted cycloheptatriene gave CHT based products. However, when electron withdrawing -CN group was attached to C-7 position of CHT we obtained norcaradiene based products. We have also observed that there exist an equilibrium between [3+2] addition products through 1,5-hydride shift. In addition, we obtained dihydrofurane derivatives in the presence of Mn(OAc)3 from compounds which have already formed C-C bond between 1,3- dicarbonyl and alkene. Formation of dihydrofurane derivatives from these compounds brought up two questions / whether cyclization is going over oxygen atom or not and whether reaction involves a cyclopropane intermediate or not. Despite all efforts, we could not manage to synthesize the required material for the investigation of these questions.

Pyrazoles constitute one of the most important classes of heterocyclic compounds due to their interesting chemical and biochemical features. Researchers have studied many pyrazole containing structures for almost over a century in order to investigate the various biological activities possessed by these molecules. A new and important trend in these studies is to produce ferrocenyl substituted pyrazoles since ferrocene attracts considerable interest in the research field of organometallic and bioorganometallic chemistry because of its valuable chemical characteristics like high stability, low toxicity and enhanced redox properties. Moreover, the results of the studies focusing on ferrocenyl compounds have been quite promising. Therefore, the scope of this project involves the combination of the essential structural features of pyrazoles with a ferrocene moiety, which could provide new derivatives with enhanced biological activities. In the course of the project the synthesis of new pyrazole derivatives was performed through Sonogashira and Suzuki-Miyaura cross-coupling reactions of 5-ferrocenyl-4-iodo-1-phenyl-1H-pyrazole with terminal alkynes and boronic acids respectively in the presence of a catalytic amount of PdCl2(PPh3)2. Although Sonogashira and Suzuki-Miyaura coupling reactions are well known in literature, they were not studied in much detail with multi-substituted pyrazoles. This also revealed the requirement of the reinvestigation of the reactions and improvement of the yields of pyrazoles by optimizing the reaction conditions.

Synthesis of five-membered heteroaromatic compounds such as pyrazoles, isoxazoles and 1,2,4-oxadiazoles are important for pharmaceutical industry and material science due to their applications. Although there are many methods to prepare such compounds, new variants continue to appear since they exhibit a wide range of biological and medicinal activities. In this thesis, new methods were developed for the synthesis of 4-iodopyrazoles, pyrazoles, isoxazoles, 1,2,4-oxadiazoles and/or 1,2,4-oxadiazepines. In the first part of the study, electrophilic cyclization of &alpha / ,&beta / -alkynic hydrazones by molecular iodine and copper iodide were investigated as new ways for the synthesis of 4-iodopyrazoles and pyrazoles, respectively. Initially, &alpha / ,&beta / -alkynic hydrazones were prepared by the reactions of propargyl aldehydes and ketones with hydrazines. Then &alpha / ,&beta / -alkynic hydrazones were treated with molecular iodine in the presence of NaHCO3, which afforded 4-iodopyrazoles in good to excellent yields. Subsequently, the same reactions were carried out with CuI in the presence of NEt3, which furnished corresponding pyrazoles in good yields. Moreover, ferrocenyl-substituted 4-iodopyrazoles and pyrazole derivatives were synthesized from corresponding