Over the years, Friedel-Crafts (FC) reactions have been acknowledged as the most useful and powerful synthetic tools for the construction of a special kind of carbon-carbon bond involving an aromatic moiety. Its stoichiometric and, more recently, its catalytic procedures have extensively been studied. This reaction in recent years has frequently been used as a key step (steps) in the total synthesis of natural products and targeted complex bioactive molecules. In this review, we try to underscore the applications of intermolecular and intramolecular FC reactions in the total syntheses of natural products and complex molecules, exhibiting diverse biological properties.

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Biomimetic syntheses of three polycylic polyprenylated acylphloroglucinol natural products isolated from Hypericum papuanum, ialibinone A, ialibinone B, and hyperguinone B, have been accomplished by selective oxidative cyclizations of the proposed biosynthetic precursor 5, which was synthesized from phloroglucinol in three steps.

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The selective one-pot conversion of enol silyl ethers into α-bromoenones allows a direct preparation of a tricyclic intermediate to papuaforin A.

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Five new prenylated tricyclic and three new bicyclic acylphloroglucinol derivatives have been isolated by bioactivity-guided fractionation of the petroleum ether extract of the dried aerial parts of Hypericum papuanum. The tricyclic compounds (1--5) were named papuaforins A--E. The bicyclic compounds were isolated together with their corresponding tautomers and were named hyperguinones A and B (6/6a,7/7a) and hyperpapuanone (8/8a), respectively. Their structures were elucidated on the basis of extensive 1D and 2D NMR experiments, as well as mass spectrometry. Furthermore, the cytotoxicity toward KB nasopharyngeal carcinoma cells and the antibacterial activity of the isolated compounds were determined.

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Bioactivity-guided fractionation of the petroleum ether extract of the aerial parts of Hypericum papuanum led to the isolation of five new tricyclic phloroglucinol derivatives. On the basis of extensive 1D and 2D NMR experiments as well as MS studies, their structures were elucidated as the C-3 epimers of 8-hydroxy-4,4, 7-trimethyl-9-(2-methylpropionyl)-3-(1-methylvinyl)-5beta -H-tricyclo[ 5.3.1.0(1,5)]undec-8-ene-10,11-dione (1,2); the C-3 epimers of 8-hydroxy-4,4, 7-trimethyl-9-(2-methylbutyryl)-3-(1-methylvinyl)-5beta-H-++ +tricyclo[5. 3.1.0(1,5)]undec-8-ene-10,11-dione (3, 4), and 8-hydroxy-4,4, 7-trimethyl-9-(2-methylpropionyl)-5beta-H-tricyclo[5.3 .1.0(1, 5)]undec-8-ene-10,11-dione (5), and their corresponding tautomers (1a, 2a, 3a, 4a, 5a). Compounds 1/1a-5/5a were named ialibinones A-E, respectively. Compounds 1/1a-4/4a showed antibacterial activity against Bacillus cereus, Staphylococcus epidermidis, and Micrococcus luteus.

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