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The total synthesis of ±-[beta]-panasinsene

University of British Columbia

This thesis describes a total synthesis of the sesquiterpenoid (±)-β-panasinsene (31). Two different routes for the synthesis of a bicyclic enone of general structure 74 were investigated. An unsuccessful attempt to generate a synthetically useful enone 74 employed the Pauson Khand cyclization of an enyne 75 (R= Me; XX= S(CH2)3S(CH or MeS, ρ-MeC6H4SO2). A second approach, which was based on the Weiss-Cook condensation of glyoxal (44) with dimethyl 3-oxoglutarate (45) led to the production of the dione 43, which was converted, via several steps, into the enone 159. The enone 1 59 was subjected to a methylenecyclohexane annulation sequence. Thus, copper (I)-catalyzed conjugate addition of the Grignard reagent 7 to 159, followed by intramolecular alkylation of the resultant chloro keto ester, provided the tricyclic intermediate 171. Sequential reduction of the keto function in 171, deoxygenation of the resultant hydroxyl function, and hydrolysis of the ketal moiety gave rise to the keto ester 182. Subjection of 182 to a photochemical Wolff ring contraction reaction sequence provided a mixture of the diesters 200 and 201. Alkylation of the mixture of 200 and 201 with methyl iodide, followed by a reduction-oxidation sequence, gave the dialdehyde 217. Wolff Kishner reduction of 21 7 resulted in the simultaneous deoxygenation of both of the carbonyl groups and successfully completed the synthesis of (±)-β-panasinsene (31).

Thesis/Dissertation

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2009-01-05

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http://hdl.handle.net/2429/3358

Chemistry

University of British Columbia

UBCV

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