Heliannuols are a unique class of Benzoxacyclic Allelopathic Sesquiterpenes
obtained from sunflowers. Allelopathy has been a keen point of interest for researchers
and represents a novel but unexplored “Methodology of self-defense mechanism”. Heliannuols
exhibit a varied structural pattern of five to eight fused benzoxacycles. Isolation
as well as synthesis of eleven members of this group namely heliannuol A to heliannuol L
has already been reported. Helianane was initially thought to be a unique member of this
group containing an eight-membered benzoxocane framework. The Ring closing Metathesis
(RCM) has been explored to a great extent amongst the synthetic intrigues undertaken
towards this category of natural products. Recent synthetic approaches and structural studies
have demanded for an amendment of helianane to curcudiol, and a tetrahydrobenzofuran
ring framework for heliannuol G and H rather the earlier predicted benzoxocane
ring system. Albeit, it is perceived that the underlying unexplored directions regarding the structural anomaly
have been highlighted in this review. The review explains exciting synthetic intrigues, bioactivity and structural
amendment and the probable perplexity of this class of novel benzoxacyclic sesquiterpenes.
Keywords: Heliannuols, synthesis, structural anomaly, ring-closing metathesis, benzoxacycles, tetrahydrobenzofuran ring.
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