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Identifier

000381019

Title

Σύνθεση [5,5,6]-δισπειροκεταλών, Ν-πολυκυκλικών και Ν-σπειροκυκλικών γ-λακταμώνμε φωτοεξείδωση απλών φουρανίων

Alternative Title

Synthesis of [5,5,6]-bis Spiroketals, N-bearing polycycles and N-spirocyclic G-lactams via photooxidation of simple furans

Author

Αντωνάτου, Ειρήνη

Thesis advisor

Βασιλικογιαννάκης, Γεώργιος

Abstract

At the outset, we hoped to employ a singlet oxygen-mediated cascade reaction sequence in order to synthesize, in one-pot, the intact [5,5,6]-BCD-bis-spiroketal ring fragment found in the family of bioactive marine toxins, the spirolides. Our first goal was the synthesis of the basic skeleton of the BCD-ring system of 13-desMeC. A onepot procedure for the formation of the [6,5,5]-bis-spiroketal moiety has been developed. The key step in this synthetic strategy was a versatile cascade reaction sequence initiated by the [4+2] cycloaddition of singlet oxygen with an easily accessible furan precursor. Having established how we could construct the BCD fragment, we set about to investigate an enantioselective, synthesis of the C11-C23 bis-spiroketal fragment of 13-desmethyl spirolide C, with the idea that this could potentially then be applied to a highly efficient total synthesis of the natural product. The synthesis of the furan precursor involved, as key steps, a Wittig reaction and alkylation of a furyl anion. In the second chapter of my Master’s research, a novel and powerful cascade reaction sequence is introduced that transforms simple furan substrates into highly complex Nbearing scaffolds that are useful in synthesis, or that are found as is in a wide variety of natural products possessing interesting biological activity. The cascade reaction sequence is initiated by the highly selective and green reagent, singlet oxygen and an exceptional and rapid increase in molecular complexity is seen in a single easy to perfom operation. The key intermediate of this new methodology is an N-acyliminium ion (NAI), which is generated in an entirely novel way during the cascade reaction sequence and is then encouraged to undergo one of two types of intramolecular cyclisation under acidic conditions (in situ); an 6-endo cyclisation of the NAI with a pendent aromatic nucleus, or trapping with a tethered nucleophile heteroatom or π- system. In this way, we have achieved rapid access to advanced N-bearing aromatic polycycles, as well as, an array of bicyclic lactams.

Language

Greek

Subject

Cascade reactions

Erythrina alkaloids

N-acyliminium

N-ακυλο-ιμινικό ιόν

Pictet-Spengler

Singlet oxygen

Spiroaminals

Spirolides

Αλκαλοειδή erythrina