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Total synthesis of certain hydrochrysene analogues Inaba, Tadanobu

Abstract

A sequence leading to the total synthesis of certain derivatives in the 11, 12-seco (see XXIV) and 5, 6-seco hydro-chrysene (see XXXI) series is described. The synthesis employs in its initial stages the Robinson-Mannich base reaction and the Michael condensation reaction to construct the parent tetracyclic skeleton. Condensation of 6-methoxy-2-tetralone with 1-diethylamino-3-pentanone methiodide produced an isomeric mixture of tricyclic ketones. This mixture was then condensed with methyl vinyl ketone to yield a tetracyclic ketol (XII) which in turn was converted to the tetracyclic ketone (XIII) by reaction with sodium methoxide. By appropriate modifications, this latter substance may then be utilized for the synthesis of a variety of hydrochrysene analogues. Oxidation of trans-anti-trans-2-methoxy-8β-acetoxy-10a -methyl-4b, 5, 6, 6a, 7, 8, 9, 10, 10a, 10b, 11, 12-dodecahydrochrysene (XVI) with t-butyl chromate solution gave not only the 12-keto derivative (XIX), but the 5-keto octahydrochrysene analogue (XX) as well as small amounts of the octahydrochrysene (XVII) and the hexahydrochrysene analogue (XVIII). The olefinic bond at the 11, 12 position of ring C (XXII) was introduced by reduction of the 12-keto derivative (XIX) with sodium borohydride, followed by dehydration with phosphorus pentoxide. Subsequent ozonization of XXII yielded the dialde-hyde (XXIV). The olefinic bond at the 5, 6 position of ring B (XVIII) was introduced by the same procedure as in the ring C series. This hexahydrochrysene analogue (XVIII) was reacted with osmium tetroxide to provide the diol (XXVI), which upon treatment with periodic acid yielded the aldol condensation product directly without isolation of the dialdehyde. Nuclear magnetic resonance (n. m. r.) spectroscopy was found to be a powerful tool for the purpose of the characterization of these rather complex molecules.

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