Approaches to the synthesis of the bicyclic fragment of the kaurane derived diterpenes.
Item
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Title
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Approaches to the synthesis of the bicyclic fragment of the kaurane derived diterpenes.
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Identifier
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AAI8914806
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identifier
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8914806
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Creator
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Yiannikouros, George Petros.
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Contributor
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Adviser: Vernon Box
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Date
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1988
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic
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Abstract
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Developments in the free radical chemistry through the decades have come with exponential growth, and the application of free radical reactions to carbocyclization has emerged as a widely used carbon-carbon bond formation method in organic synthesis.;A new method is described for the synthesis of fused and bridged ring systems based on the intramolecular addition of a vinyl radical to an {dollar}\alpha{dollar},{dollar}\beta{dollar}-unsaturated ketone. The method represents a general route to masked {dollar}\gamma{dollar}-diketones. In this approach a vinyl radical formed by trialkyltin hydride mediated homolysis of a vinyl halide, undergoes internal addition to a stereoproximal alkene moiety, followed by a hydrogen transfer to the addend radical.;The efficiency of the ring formation is enhanced by the kinetic preference of the vinyl radical to undergo addition to the radical acceptor alkene moiety, over the transfer of the hydrogen atom from the organostannane. This method illustrates the successful utilization of vinylogous reactivities in a radical addition to {dollar}\alpha{dollar},{dollar}\beta{dollar}-enones, and proceeds in regioselective manner. In order to delineate the relationship between the substitution pattern of the acceptor alkene moiety and the mode of ring closure, substituted enones were subjected to carbocyclization. The utility of this annulating method in the synthesis of natural products was demonstrated by the syntheses of several highly functionalized, bridged bicyclic systems which were precursors for several terpenoids possessing antitumor and antifertility activity.;A significant part of our investigation includes the development of simple and general methods for gaining access to starting materials that are properly constituted to undergo the radical ring closure. The effort to prepare such materials demonstrated the value of the Birch reduction-alkylation sequence in the construction of the required properly substituted cyclohexenones.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
