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Synthesis of jasmonoids : Synthesis of cyclic ketal-type insect pheromones

University of British Columbia

This thesis consists of two parts. Part I describes the preparation of cyclopentenones using trimethylsilylpropyne as an acetonyl unit, and its application to the synthesis of cis-jasmone (1) and dihydrojasmone (3) . β-Keto ester dianions were alkylated at the γ-carbon with 3-bromo-l-trimethylsilyl-1-propyne. The resulting alkynes were hydrated to give the 1,4-diketo compounds which were then cyclized to the corresponding cyclopentenones, cis-jasmone (1) and dihydrojasmone (3) . Part II describes the synthesis of various cyclic ketal insect pheromones, viz., frontalin (17) , endo-brevicomin (16) , exo-brevicomin (15) , (-)-α-multistriatin (18α) and lineatin (22) , which have considerable economic values due to their potential utility in the control of beetle population. The dianion of methyl acetoacetate was alkylated with homoallylic bromides. The resulting alkenes were epoxidized and then cyclized with a Lewis acid to produce esters containing the 6,8-dioxabicyclo[3.2.1]octane skeleton. These esters were hydrolyzed and decarboxylated. This methodology was utilized in a synthesis of frontalin (17) and stereospecific syntheses of endo-brevicomin (16), and exo-brevicomin (15). In addition, one of the intermediates in the synthesis of 15 was partially resolved, leading to optically active exo-brevicomin. A chiral synthesis of (-)-α-multistriatin (18α) was accomplished using methyl α-D-glucopyranoside (7i) as starting material. Methyl 4,6-0-benzylidene-2,3-dideoxy-2-C-methyl-α-D-arabino-hexopyranoside (197) was prepared in six steps from methyl α-D-glucopyranoside (71) . The benzylidene 197 was converted into the alkene 207. Then the methyl group at C-4 in the intermediate 201 was generated by a stereoselective hydro-genation of 207 using Wilkinson's catalyst. The dithiane derivative 219 was used to effect both introduction of the ethyl side-chain and the cyclization to form the bicyclic ketal skeleton. The spectral data of the synthetic (-)-α-multistriatin (18α) was found to be identical with those for the natural compound. A synthesis of lineatin (22) is also described. The cis fused bicyclo[4.2.0] ring system in 22 was constructed via a photocycloaddition reaction involving 3-methyl-5-hydroxy-2-pentenoic acid 6-lactone 119 and allene. A mixture of regio-isomers 233 and 234 was obtained in a ratio of 5:3. This mixture was used throughout the subsequent reactions and the final isomeric products lineatin (22) and 23 were separated by column chromatography. The present route to lineatin (22) represents a major improvement over the previous syntheses in terms of efficiency and stereoselectivity. [See thesis for Chemical Diagrams]

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2010-03-15

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http://hdl.handle.net/2429/21910

Chemistry

University of British Columbia

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