## 3 Chemistry and Biological Activities of Selected Meroterpenoids
Alternatively, compound **17** was treated with MeI to protect the secondary hydroxyl group, and the aromatic methoxy group was revealed under thio-anion reaction conditions to yield compound **19** in excellent yields. The resultant compound **19** was oxidized at the alpha phenol with IBX followed by reduction with NaBH4 of the newly formed ortho-diketone to provide the natural product corysoriol J (**100c**). In parallel efforts, compound **13'** was subjected to carbonyl-reduction followed by LiAlH4 or amine borane reagent to enhance the diastereoselectivity yielding alcohols **20** and **20'** in 6.5:1 or 18:1 ratio respectively. Deprotection of compound **14** mediated by thio-anion treatment under heat led to natural product (\(-\))-corysoriol H (**100e**), which upon two-step sequence epoxidation mediated by _m_CPBA and subsequent reductive opening of the epoxide with LiAlH4 provided (\(-\))-8\(\alpha\)-hydroxy-cyclobakuchiol C (**100g**). In a similar fashion, intermediate **20** was subjected to methyl-protecting group maneuver via intermediate **21**, followed by one-pot oxidation mediated by IBX and subsequent reduction of the newly formed ortho-diketone. This, mediated by NaBH4 yielded corysoriol I (**100h**). Finally, methyl deprotection of compound **20'** mediated by thermal treatment in the presence of thio-anion yielded (\(-\))-posaroacrylifol G (**100f**). The short and efficient synthetic strategy enables access to a large number of natural products, which can be further investigated for their biological properties. Figure 5: Structures of representative meroterpenoids. Rhodomyrtone belongs to a large and diverse family of tricyclic meroterpenoid systems isolated from _Rhodomyrtus tomentosa_[66; 67; 68; 69; 70]. This set of compounds has been shown to have strong antibacterial activity, acting primarily against gram-positive strains. In addition, the combined extracts of _Rhodomyrtus tomentosa_ have shown anti-cancer and anti-tumoral effects in various models [66; 67]. The synthesis of the unusual cryophyllene-derived meroterpenoids (CDMTs) including rhodotomentone A (**127**) and rhodotomentone B (**128**) was reported via a biomimetic pathway [68; 69; 70], (Scheme 2). The synthesis began from the natural product leptospermome (**22**), a commonly occurring acylphoroglucinol, which was subjected to dehydration mediated by DIBAL-H, yielding the dearomatized _ortho_-quinone methide (\(o\)-QM) intermediate **23** in gram-scale. This maneuver was followed by a [4+2] Diels-Alder photo-cycloaddition reaction with singlet oxygen, generated under blue LED (455 nm) radiation to provide endoperoxide intermediates **24a** and **24b** in 1:1 ratio. The formed \(o\)-QM intermediate **23** was subsequently subjected to hetero-Diels-Alder (HDA) reaction with \(\beta\)-caryophyllene **25** to produce a mixture of rhodomentone A (**115**), and the related natural products, tomentodione A, B, C and D (**116**, **117**, **118**, and **119**). Rhodomentone A (**115**) can be treated with endoperoxide **24b** to undergo the key Kornblum-DeLamare rearrangement and Diels-Alder cycloaddition reaction sequence under thermal reaction conditions. This produces rhodotomentone A(**127**) and B(**128**), along with two other rhodotomentone diastereoisomers, compounds **27** and **28**. Additionally, endoperoxide **24b** was reacted with \(\beta\)-caryophyllene (**25**) to undergo the Kornblum-DeLamare rearrangement and Diels-Alder cycloaddition reaction sequence under thermal conditions to generate rhodomentodine A, B, Q and R (**123**, **124**, **125** and **126**), along with rhodomyrtusial A, B and C (**120**, **121** and **122**) and compound **29**[70]. In an efficient approach (Scheme 3), CDMTs **123**, **124**, **125** and **126** were easily converted to the corresponding natural products rhodomentone A (**127**), **28**, rhodomentone B (**128**) and **27** respectively. This was carried out under hetero-Diels-Alder (HDA) reaction conditions, requiring Lewis acid, ZnI\({}_{2}\) and heat, in relatively modest yields.