Submitted to: Synthetic Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2008
Publication Date: April 15, 2009
Citation: Petroski, R.J., Bartelt, R.J., Vermillion, K. 2009. Synthesis of a Dimethylfuran Containing Macrolide Insect Pheromone. Synthetic Communications. 39:1389-1405. Interpretive Summary: Previously, a novel pheromone was identified from the beetle species Galerucella calmariensis and G. pusilla. These species were introduced into North America from Europe as biological control agents for the invasive wetland weed, purple loosestrife (Lythrum salicaria), and have had significant success in suppressing this noxious plant. A practical need is for land managers to be able to monitor beetle populations, and the pheromone is useful for this purpose. An improved synthetic pathway to the pheromone was developed to help meet that need. The synthetic pathway to the pheromone of Galerucella beetles was shortened from 13 to just 10 steps, and the overall yield was increased sixfold. These improvements should aid the practical availability of this pheromone.
Technical Abstract: The synthetic pathway to the furan-containing macrolide pheromone of Galerucella beetles was shortened from 13 steps in the original synthesis to 10 steps, and the overall yield was increased greater than six fold. A concise Reformatsky-based sequence of reactions was utilized to construct the key precursor, 2,3-dimethyl-2-butenolide. Reduction of the butenolide with diisobutylaluminum hydride afforded 3,4-dimethylfuran. A one-pot sequence of lithiation, alkylation by a THP-containing iodide, a second lithiation, and finally, formylation gave the required tetrasubstituted furan intermediate, 3,4-dimethyl-5-[5-(tetrahydrofuran-2-yloxy)pentyl]-2-furaldehyde. To continue construction of the 3-carbon acyl side chain, the aldehyde was converted to an unsaturated ester by a Horner-Wadsworth-Emmons (HWE) condensation with triethyl phosphonoacetate. After reduction of the double bond in the ester side chain and removal of protective groups, the lactone ring was closed using the Mitsunobu method, which is milder, simpler, and could be accomplished with less solvent than the previous (Yamaguchi) method. The pheromone can be used to monitor populations of G. calmariensis and G. pusilla (Coleoptera: Chrysomelidae), which have been introduced into North America as biological control agents for the invasive wetland weed, purple loosestrife (Lythrum salicaria).