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Studies on total synthesis of veratrum alkaloids

University of British Columbia

The initial work toward a synthetic entry into the hexacyclic cevane nucleus (7) is described, and the specific application of this work to the total synthesis of verticine (12) is discussed. Hecogenin acetate (74) was converted to C-nor-D-homo-(25 R)-5α-spirost-13(18)-en-3β-ol-3-acetate (79) via a known procedure, and hydroboration of the double bond gave the corresponding 13β-hydroxymethyl compound (80(a)). The mass spectral fragmentation of the spiroketal system is discussed. The stereochemistry at C-13 of the hydroborated compound (80(a)) was reversed by oxidation of the primary alcohol to the aldehyde, epimerization, and reduction. Acetylation gave the diacetate (85) which was used in investigation of the spiroketal side chain degradation. The Baeyer-Villiger oxidation sequence developed by W.F. Johns was used in the spiroketal degradation. 13α-Acetoxymethyl-17-acetyl-18-nor-5α-etiojerv-16(17)-en-3β-ol-3-acetate (110) was obtained with considerable difficulty in low yield from this sequence, A model compound, 17-acetyl-5α, 13β-etiojerv-16(17)-en-3β-ol (111), was employed to test the feasibility of attachment of a heterocyclic portion via a reaction developed by Schreiber and Adam. Reduction of the double bond and epimerization of the methyl ketone gave the ketone (120), which was then condensed with 2-lithio-5-methylpyridine. The structure of the condensation product was established by its n.m.r. and mass spectra.

Text

2011-05-13

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http://hdl.handle.net/2429/34565

Chemistry

University of British Columbia

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