A phloroglucinol‐terpene adduct (PTA) collection consisting of twenty‐four molecules featuring three skeletons was discovered from Baeckea frutescens. Inspired by its biosynthetic hypothesis, we synthesized this PTA collection by reductive activation of stable phloroglucinol precursors into highly reactive ortho‐quinone methide (o‐QM) intermediates and subsequently Diels–Alder cycloaddition. We also demonstrated, for the first time, the generation process of the active o‐QM by performing dynamic NMR and HPLC‐MS monitoring experiments. Moreover, the PTA collection showed significant antifeedant effect toward the Plutella xylostella larvae. Insight of nature: A phloroglucinol‐terpene adduct (PTA) collection was discovered from Baeckea frutescens. The plausible biogenetic pathway, biomimetic synthesis, generation mechanism, and feeding deterrent activity of the PTA collection were also investigated. The current study first provided experimental evidence to explain how, and perhaps why, plants apply a combinatorial strategy to create the PTA collection (see figure).