No description available.

No description available.

No description available.

No description available.

Formation of carbon–fluorine and carbon–fluoroalkyl bonds via transition metal complexes represents an efficient synthetic route towards a wide array of valuable fluorinated organic compounds and fluorinated metallacycles offer a potentially green and atom economical pathway towards these functionalized fluorocarbons. This thesis is focused on cycloaddition reactions of Ni=CF2 complexes with fluoroalkenes (FAs) and acetylenes. Cycloaddition reactions of the FAs vinylidene fluoride (CF2=CH2) and perfluoro(methyl vinyl ether) [CF2=CF(OCF3)] with the electron-rich Ni(0) fluorocarbene, Ni=CF2[P(OMe)3](dppe) affords stable metallacyclobutane complexes, likely through a 1,4-diradical mechanism previously investigated for analogous reactions using computational chemistry. With CF2=CHF (TrFE), however, the observed products are the C3 alkene E-CHF=CF(CF3) and the metallacyclopentane complex, Ni(C4H2F6)(dppe), derived from oxidative coupling of two additional equivalents of TrFE. It is proposed that the instability of the initially formed metallacyclobutane gives rise to a 2,1-F shift, yielding the C3 alkene complex. Reaction of the latter with excess TrFE then liberates the C3 alkene, forming the TrFE alkene complex followed by the observed metallacyclopentane product. In the reaction of 1a with chlorotrifluoroethylene (CF2=CFCl) a single regioisomer of the metallacyclobutane is observed, but reacts further in THF solvent via α-Cl migration to Ni, affording the tetrafluoroallyl complex, NiCl(CF2CF=CFH), in which one F has been replaced by a hydrogen. Finally, reaction of 1a with hexafluoropropene [CF2=CF(CF3), HFP] takes an unprecedented turn, affording the Ni trifluoromethyl perfluoroalkenyl complex from formal transfer of one F from HFP to the Ni=CF2 moiety. The capability of 1a to perform cycloaddition with a broader substrate scope was investigating by reacting it with terminal aryl-acetylenes of varying electronic parameters. Reaction of 1a with 1.5 equivalents of 4-R-phenylacetylene afforded the expected difluorometallacyclobutenes (R = H, Cl, tBu). Further observation revealed a second acetylene insertion to yield a nickelacyclohexadiene in the first example of a 4- to 6-membered ring expansion of perfluorometallacycles. The six-membered metallacycle then undergoes reductive elimination to furnish a difluorocyclopentadiene. The electronic parameters of the aryl-acetylene substrate play a dramatic role in the selectivity of product formation. The more electron-donating substrates 4-tert-butylphenylacetylene and 1-hexyne stabilize the metallacyclobutene, while the electron-withdrawing 4-chlorophenylacetylene affords a more reactive metallacyclobutene making it more prone to the second acetylene insertion. Phenylacetylene represented a middle-ground between the two systems and proved effective for further characterization studies. The electronic effect of the surrounding ancillary ligand system was also studied by substituting dppe in 1a for P(OMe)3 and dipe to give analogous Ni(0) difluorocarbene complexes 1b and 1c (dipe = 1,2-bis(diisobutylphosphino)ethane). The -acidic phosphite ligands in 1b gave exclusively nickelacyclohexadiene and difluorinated cyclopentadiene due to a reactive metallacyclobutene, whereas the more electron rich 1c formed the metallacyclobutene product almost exclusively. The results presented here will allow for future investigations of fluorinated metallacycle reactivity, increasing our ability to prepare value-added fluorocarbon products for pharma, agrochemicals, and polymer applications.

This study deals with the (4+2)-cycloaddition reactions of 4-π electron compounds with ketenes. Chloroketenes were generated in situ from the corresponding chlorinated acid chlorides in the presence of the ketenophiles. Chloro-, dichloro- and diphenylketenes reacted with 1-methoxy-3-trimethylsiloxy-l,3-butadiene, and 2,4-bis(trimethylsiloxy)-1,3-pentadiene to yield the corresponding dihydropyrans. The dihydropyrans yielded substituted 4-pyranones on hydrolysis.

The purpose of this investigation was to study the chemistry of the new and novel (trimethylsilyl)ketene. This ketene was synthesized by pyrolysis of (trimethylsilyl)ethoxyacetylene which was prepared from ethoxyacetylene and methyllithium. (Trimethylsilyl)ketene is a very stable and isolable ketene which does not dimerize and, therefore, provides an opportunity for some unique studies that have not been possible with other monosubstituted ketene.

Les alcaloïdes sont, en général, une famille de composés hétérocycliquesd'origine végétale qui intègrent des atomes d'azote dans leur structure complexe.Leur intérêt réside dans les activités biologiques intéressantes qu'ils présentent, etpour cette raison, ils sont largement utilisés par l'industrie pharmaceutique. Enparticulier, les anneaux de pyrrolidine et de pipéridine se trouvent comme basefondamentale dans un grand nombre de telles structures. D'autre part, l'un desprincipaux objectifs de la chimie synthétique est d'obtenir ces types de moléculesd'une manière asymétrique. Entre autres, la catalyse métallique s'est révélée trèsutile à cet effet. Par exemple, les ligands de type ferrocényle précédemmentdéveloppés dans notre groupe donnent naissance à des pyrrolidines énantiopuréesdensément substituées. De même, ces types de ligands ont été évalués dansdifférents types de réactions de cycloaddition, ce qui a entraîné la formationasymétrique de structures tricycliques d'intérêt biologique. D'autre part, une synthèseracémique collective de composés tétracycliques de la famille Securinega a étédéveloppée. Cette synthèse permet d'accéder à différents produits naturels de lafamille en raison de la polyvalence de l'intermédiaire lactone bicyclique. / Alkaloids are, in general, a family of heterocyclic compounds of vegetal originthat incorporate nitrogen atoms in their complex structure. Their interest lies in theoutstanding biological activities they present, and for this reason they are widely usedby the pharmaceutical industry. In particular, pyrrolidine and piperidine rings arefundamental scaffolds found in a large number of such structures. On the other hand,one of the main objectives of synthetic chemistry is to obtain these types ofmolecules in an asymmetric way. Among others, metal catalysis has proven to bevery useful for this purpose. For example, ferrocenyl proline ligands previouslydeveloped in our group gave rise to densely substituted enantiopure pyrrolidines.Likewise, these types of ligands have been evaluated in different types ofcycloaddition reactions, which have resulted in the asymmetric formation of tricyclicstructures of biological interest. In contrast, a collective racemic synthesis oftetracyclic compounds of the Securinega family has been developed. This synthesisprovides an access to different natural products of the family due to the divergencegiven by a bicyclic lactone intermediate.

No description available.

No description available.