Synthesis and absolute configuration of (S)-(+)-chichimol ketone: the defensive secretion of walking stick Agathemera elegans

The first enantioselective synthesis of chichimol ketone (4-methyl-1-hepten-3-one) is described and the absolute configuration of the main semiochemical compound is determined as having an (S)-configuration. The synthesis features the use of a ruthenium catalytic asymmetric hydrogenation reaction to introduce chirality into acid 2. The synthetic chichimol ketone (S)-1 displayed a specific rotation that was in accordance with that of the natural product, thereby supporting the (S) configuration for natural chichimol ketone. To assure the correct stereochemical assignment, (S)-1 was converted in the known ketone (S)-5: the main alarm pheromone of the ant Atta texana that is 400 times more active than its (R)-enantiomers.