Browsing by Author "Rauhala, Vesa"

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  • Conversion of carbonyl compounds to alkynes: general overview and recent developments
    (2010) Habrant, Damien; Rauhala, Vesa; Koskinen, Ari M.P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The preparation of alkynes from carbonyl compounds via a one-carbon homologation has become a very useful pathway for the synthesis of acetylenic compounds, both internal and terminal. This tutorial review provides an overview of the different methods available for this transformation, including their scope and limitations, recent developments and applications in total syntheses.
  • An expedient synthesis of spiroketals: model studies for the calylucin C16-C25 fragment
    (2004) Koskinen, Ari; Rauhala, Vesa; Nevalainen, Marta
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Anew short strategy to prepare the spiroketal fragment of calyculins is presented. A novel Seyferth–Gilbert type homologation of hindered lactols to the corresponding alkynes has been achieved for the first time. The spirocyclization was achieved efficiently via a DIHMA (double intramolecular hetero-Michael addition) process of this hindered ynone. The spirocyclization rate is not dependent on the stereochemistry of the alkoxy substituent in the oxolane ring.
  • Polyhydroksihappojen peptidikytkennät
    (2002) Passiniemi, Mikko
     Helsinki University of Technology | Master's thesis
  • The Reaction Mechanism of Spirocylization and Stereoselectivity Studies for the Calyculin C16-C25 Fragment
    (2005) Koskinen, Ari M.P.; Rauhala, Vesa; Nättinen, Kalle; Rissanen, Kari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The mechanism of the double intramolecular hetero-Michael addition, a key reaction in the planned synthesis of the natural product calyculin C, has been studied by NMR. The cyclization follows Baldwin’s rules and proceeds first through a six-membered ring closure (6-endo-dig), followed by a fivemembered ring cyclization (5-exo-trig).
  • Spirocycle fragment of calyculins
    (2007-08-25) Rauhala, Vesa
     Doctoral dissertation (monograph)
    Calyculins are highly cytotoxic metabolites and protein phosphatase inhibitors isolated from the marine sponge Discodermia calyx. Despite several research groups' efforts to synthesize naturally occurring Calyculin A or C, none has accomplished yet the fully synthetic route. The literature part includes an overview of the synthesis of triple bonds. The very basis of these methods are elimination reactions. Historically name reactions are important. They have had bigger than normal influence on synthetic chemistry since they were invented. The most important part of this section for this thesis is chapter 1.4, which presents different methods for the conversion of aldehydes, ketones and lactones to alkynes. These are the backbone of the experimental section. Finally in the selected synthesis chapter I have chosen examples, which are closely related to the topics I worked during this thesis. The experimental part presents my own results of synthetic efforts on the spiroketal part of calyculins. I succeeded to synthesize the spirocycle and proved that the cyclization rate is not critically dependent on the existence of a directing alkoxy group in the oxolane ring. I also carried out mechanistic studies for the spirocyclization mechanism. Results prove that the mechanism follows Baldwin's rules for ring closure.