Two new natural products, N‐(2‐methyl‐3‐oxodec‐8‐enoyl)‐2‐pyrroline (2) and 2‐(hept‐5‐enyl)‐3‐methyl‐4‐oxo‐6,7,8,8a‐tetrahydro‐4H‐pyrrolo[2,1‐b]‐1,3‐oxazine (3), have been isolated from Penicillium brevicompactum Dierckx. Compound 2 has shown an important in vivo anti‐juvenile‐hormone (anti‐JH) activity while compound 3 has exhibited insecticidal activity against Oncopeltus fasciatus Dallas. Both products have been synthesized starting from 1,4‐hexadiene, by means of a sequence of reactions which includes the preparation of 6‐octenoic acid and its transformation into the corresponding acid chloride, in order to acylate Meldrum's acid. Subsequent aminolysis with pyrrolidine, followed by methylation at the activated position of the β‐oxo amide with iodomethane, introduction of a methoxy group at the pyrrolidine ring by anodic oxidation and final elimination of methanol on SiO2 led to 2 and 3. The fact that both metabolites can be prepared by the same sequence indicates that they must be biogenetically related. Based on structural similarities, compounds 2 and 3 are also closely related to the recently discovered brevioxime (1).