A Suite of Novel Allenes from Australian Melolonthine Scarab Beetles. Structure, Synthesis, and Stereochemistry

A suite of allenic hydrocarbons, previously unknown as a molecular class from insects, has been characterized from several Australian melolonthine scarab beetles. The allenes are represented by the formula CH3(CH2) n CH•CH(CH2)7CH3 with n being 11−15, 17 and 19, and thus, all have Δ9,10-unsaturation. These structures have been confirmed by syntheses and comparisons of spectral and chromatographic properties with those of the natural components. The enantiomers of (±)-Δ9.10-tricosadiene and Δ9,10-pentacosadiene were separable on a modified β-cyclodextrin column (gas chromatography), and the natural Δ9,10-tricosadiene (n = 11) and Δ9,10-pentacosadiene (n = 13) were shown to be of >85% ee. Syntheses of nonracemic allenes of known predominating chirality were acquired using both organotin chemistry and sulfonylhydrazine intermediates, and comparisons then demonstrated that the natural allenes were predominantly (R)-configured.