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Studies on the biological activity of synthesised lactones revealed high selectivity towards insect pests as well as bacterial strains. Only the halolactones exhibited significant antifeedant activity. In contrast, antibacterial activity was shown only by the lactone (8) without halogen.

Two δ‐iodo‐γ‐lactones and two γ‐iodo‐δ‐lactones substituted at the β‐position with phenyl or 4‐methylphenyl ring have been synthesized in both enantiomeric forms. The starting materials were enantiomerically enriched allyl alcohols with an (E)‐4‐phenylbut‐3‐en‐2‐ol system (ee in the range 88–99 %), which were obtained by lipase‐catalyzed transesterification. Alcohols were subjected to orthoacetate modification of the Claisen rearrangement. The high stereoselectivity of this reaction led to retention of (E)‐configuration of the double bond and complete transfer of chirality from the allyl alcohol to the benzylic position C‐3. As a result, chiral γ,δ‐unsaturated esters with retained configuration of the stereogenic center were produced. Their hydrolysis and iodolactonization afforded new enantiomers of iodolactones with high or excellent ee (97–99 %). Their configuration at C‐4 was a direct result of the configuration at C‐3 of the acid subjected to iodolactonization, whereas stereocenters at C‐5 and C‐6 were formed as a consequence of the reaction mechanism. For most of the synthesized isomers, the predicted configurations were established by X‐ray analysis. The presented chemoenzymatic pathway represents a useful strategy that can be applied in the asymmetric synthesis of variety of lactones from 4‐arylbut‐3‐en‐2‐ols.

The results of biological tests showed that halogen atom removal significantly increased the antifeedant properties of γ-lactones with a p-methoxyphenyl substituent. Unsaturated lactones are most promising in the context of their possible industrial application as crop protection agents. Further structural modifications of lactones with aromatic rings are needed to find important structural factors increasing the antibacterial activity.

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