Since the discovery of the pentafluorosulfanyl (SF5) group around the 1960s, progress in exploring the chemistry of aliphatic SF 5-containing compounds stagnated because of a lack of efficient synthetic methods. More recent developments in the preparations of SF5-containing compounds afforded easier access to these compounds, and sparked great interest in exploring their chemistry. Chapter 1 discusses the development of efficient methods used to prepare SF5-containing aliphatic compounds.
This dissertation investigates the combination of steric and polar effects of pentafluorosulfanylation on aliphatic molecules. Chapter 2 discusses the synthesis and chemistry of aliphatic aldehydes and aldimines containing the SF5 group in the 2-position. The aldehydes undergo many of the common chemical transformations of aliphatic aldehydes, affording a variety of SF5-containing compounds. The large C–S bond dipole helps direct additions to the carbonyl group in a manner consistent with the Cornforth hypothesis, resulting in highly diastereoselective nucleophilic additions. Similarly, the synthesis of SF5-containing SF5β-lactams by [2+2] cycloadditions of 2-pentafluorosulfanylaldimines with azidoketene proceeds with high diastereofacial selectivity. The SF5 β-lactams formed by this reaction may lead to a greater variety of diastereoselectively-prepared amino acid compounds for study in peptides, the preparation of new antibacterial compounds, and the design of novel SF5 β-lactamase inhibitors.
Chapter 3 discusses the structural studies of some synthesized pentafluorosulfanylated molecules to help further elucidate the steric and polar effects of pentafluorosulfanylation on aliphatic compounds. Coupling constant analyses determined the local molecular structure near the SF5 group and revealed that the unexpected diastereotopic resonances in 1H NMR spectra were the result of partial insertion of a hydrogen atom between two equatorial fluorine atoms, thus “locking” the conformation of the alkyl chain near the SF5 group. Computational experiments confirmed the experimentally-determined S–C–C–O dihedral angle of 85° observed in the alcohols formed by nucleophilic addition to the aldehyde carbonyl group of 2-pentafluorosulfanyl aldehydes. Computation of the reaction profile for the [2+2] cycloaddition of 2-pentafluorosulfanylaldimines with azidoketene revealed a difference in the reaction barriers leading to the two diastereomeric pairs of products of about 4.1 kcal/mol. Formation of the 1,2-lk,lk products is favored over the formation of the other possible products.
|Advisor:||Welch, John T.|
|Commitee:||Barnes, George L., Dikarev, Evgeny V., Fabris, Daniele, Musah, Rabi A.|
|School:||State University of New York at Albany|
|School Location:||United States -- New York|
|Source:||DAI-B 77/05(E), Dissertation Abstracts International|
|Keywords:||Aldehydes, Beta-lactams, Computation, Pentafluorosulfanyl, Preparation|
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