There is provided an improved process for producing biologically active arylterpenoid compounds useful to inhibit eclosion of pupae, e.g., fly pupae or mosquito pupae. The process is characterized by reacting a terpenoid material having a terminal unsaturated linkage, e.g., dihydromyrcene (3,7-dimethylocta-1,6-diene) with a lower alkyl Grignard reagent, e.g., n-propyl magnesium chloride to form a Grignard exchange product. The exchange product is then benzylated. Either a benzyl halide, e.g., p-isopropylbenzyl chloride, or a benzaldehyde, e.g., p-isopropylbenzaldehyde may be used. These compounds are specifically described in U.S. Pat. No. 4,002,769. They contain also a lower alkoxy group, e.g., methoxy. This can be introduced prior to the formation of the Grignard exchange product or at a later stage in the operation. Use of the exchange-type Grignard reaction enables elimination of several steps when producing the arylterpenoids from pinene as the terpene source, and consequent costs.