Total synthesis of (±)-heliannuol D, an allelochemical from Helianthus annuus

Synthesis of Trifluoromethylated Dibenzoxepines via Palladium-Catalyzed Tandem C-O Bond Formation/C-H Arylation

A palladium-catalyzed cyclization reaction of phenols with trifluoromethyl-containing ortho-bromo-β-chlorostyrenes has been developed. In the presence of palladium(II) acetate, tricyclohexylphosphine, and cesium carbonate, a variety of 6-trifluoromethyldibenzo[b,d]oxepines were prepared in moderate to good yields through the tandem O-alkenylation of general phenols and subsequent C-H arylation.

Base-promoted cyclization of ortho-hydroxyacetophenones with in situ generated cyclopropenes: diastereoselective access to spirobenzo[b]oxepines and related precursors

An unprecedented [5 + 2] spirocyclization route to obtain a vital class of functionalized spirobenzo[b]oxepine-cyclopropanes in good to high yields with excellent diastereoselectivities is reported. This domino reaction proceeds through a regioselective oxa-Michael addition of ortho-hydroxyacetophenones as 1,5-binucleophiles to in situ produced highly reactive cyclopropenes from 2-aroyl-1-chlorocyclopropanecarboxylates triggered by Cs₂CO₃ and the subsequent intramolecular aldol reaction under heating conditions, enabling the formation of new C-O and C-C bonds for benzo[b]oxepine ring synthesis. Moreover, at ambient temperature, the above C-O/C-C bond-forming event takes place preferentially via a [4 + 2] annulation path over a spirocyclization route, leading to substituted fused-cyclopropanes with good diastereoselectivities. Gratifyingly, further alterations of the obtained spirobenzo[b]oxepines and tetrahydrocyclopropa[b]chromenes afford fascinating classes of 4H-chromen-4-ones and cyclopenta[c]chromenes, respectively, under metal-free conditions.

Base-Free Catalytic Wittig-/Cross-Coupling Reaction Sequence as Short Synthetic Strategy for the Preparation of Highly Functionalized Arylbenzoxepinones

The facile synthesis of highly functionalized building blocks with potential biological activity is of great interest to medicinal chemistry. The benzoxepinone core structures commonly exhibit biological activity. Thus, a short and efficient synthetic route towards benzoxepine containing scaffold, which enables late stage modification was developed. Namely, base-free catalytic Wittig reactions enabled the synthesis of bromobenzoxepinones from readily available starting materials. Subsequent, Suzuki–Miyaura and Stille reactions proved to be suitable methods to access a variety of benzoxepinone diaryl derivatives by late stage modification in only three steps. This three-step reaction sequence is suitable for high throughput applications and gives facile access to highly complex molecular structures, which are suitable for further functionalization. The antiproliferative properties of selected arylbenzoxepinones­ were tested in vitro on monolayer tumor cell line A549. Notably, in this initial screening, these compounds were found to be active in the micromolar range.

Visible-light-induced radical cascade cyclization of 1-(allyloxy)-2-(1-arylvinyl)benzenes with sulfonyl chlorides for the synthesis of sulfonated benzoxepines

A visible light photocatalyzed cascade sulfonylation/cyclization of 1-(allyloxy)-2-(1-arylvinyl)benzenes with sulfonyl chlorides for the construction of sulfonated benzoxepines is developed.

Heliannuol: Distribution, Biological Activities, 1H and 13C-NMR Spectral Data

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Heliannuols are an important class of compounds isolated from Helianthus annuus, a common sunflower, with allelopathic properties. Interestingly, two of these fourteen compounds have been isolated from a gorgonian, Pseudopterogorgia rigida. This review compiles data on the isolation and biological activity of heliannuols described in the literature and briefly reports the papers describing their syntheses. This review could stimulate research into other natural species and syntheses. Further, it describes the 1H and 13C-NMR spectral data described in the literature for the 14 heliannuols already isolated and correlates them with their respective structures. Therefore, we believe that these searchable data enable a rapid identification in routine analysis of the crude extracts of sunflowers or gorgonians.

Synthesis of substituted Z-styrenes by Hiyama-type coupling of oxasilacycloalkenes: application to the synthesis of a 1-benzoxocane

Several Hiyama cross-coupling reactions of oxasilacycloalkenes and aryl iodides are described that produce trisubstituted Z-styrenes in moderate to excellent yields. Both electron-rich and electron-poor aryl iodides are tolerated in the cross-coupling reaction. The oxasilacycloalkene coupling partners were prepared by ruthenium-catalyzed intramolecular anti-hydrosilylation of alkynols. One of the cross-coupling products was converted to a 1-benzoxocane, albeit in low yield, using an intramolecular Buchwald–Hartwig etherification. The cyclic ether produced contains the carbon skeleton of heliannuol A.

Base-Promoted Formal [4 + 3] Annulation between 2-Fluorophenylacetylenes and Ketones: A Route to Benzoxepines

The first base-promoted formal [4 + 3] annulation between 2-fluorophenylacetylenes and ketones has been disclosed. The reaction proceeds through a tandem α-vinylation of ketones followed by an intramolecular nucleophilic aromatic substitution (SNAr) reaction of the in situ generated β,γ-unsaturated ketone intermediates, providing a straightforward access to a wide range of functionalized benzoxepines in moderate to high yields. The transition-metal-free methodology featured a wide substrate scope, the use of easily available starting materials, and a high functional group tolerance.

Direct, One-Step Synthesis of Condensed Heterocycles: A Palladium-Catalyzed Coupling Approach

[reaction: see text] A palladium-catalyzed one-step synthesis of fused aromatic heterocycles from bifunctional bromoenoates or bromoalkyl indoles and iodoarenes is reported. This method provides an efficient route to a wide variety of substituted polycyclic aromatic and heteroaromatic compounds from readily accessible starting materials.

Enantioselective Total Synthesis of (−)-Curcuquinone via Regioselective Chromium-Mediated Benzannulation

[reaction: see text] A short and efficient, high-yielding enantioselective total synthesis of the marine natural product (-)-curcuquinone 1 is reported involving a regioselective [3 + 2 + 1]-benzannulation reaction as the key step. Additionally, this strategy allows the isolation of curcuhydroquinone monomethyl ether 9 as an intermediate of the benzannulation reaction and its subsequent further protection toward diversified hydroquinones.

Synthesis of aromatic bisabolene natural products via palladium-catalyzed cross-couplings of organozinc reagents

Aromatic bisabolene derivatives were prepared by two methods involving cross-coupling of organozinc reagents. The first synthesis of (+/-)-glandulone A (10), as well as syntheses of (+/-)-curcuhydroquinone (8) and (+/-)-curcuquinone (9), were accomplished via coupling of a secondary alkyl zinc reagent (1,5-dimethyl-4-hexenylzinc halide, 18) to protected bromohydroquinones using Pd(dppf)Cl(2) as catalyst. Coupling of arylzinc halides with alkenyl triflate 16 using Pd(PPh(3))(4) catalyst provided a number of bisabolene derivatives and led to syntheses of dehydro-alpha-curcumene (2), (+/-)-curcuphenol (3), and (+/-)-elvirol (13). A high-yield synthesis of the (+/-)-heliannuol D precursor 29 is also reported using this method.

Plant-growth inhibitory activity of heliannuol derivatives

In addition to (+)-, (-)- and (+/-)-heliannuol E, growth-inhibitory activities of five synthetic chromans and four tetrahydrobenzo[b]oxepins were examined against oat and cress. All heliannuol E isomers exhibited similar biological activities against cress, whereas when tested against oat roots, the unnatural optical isomer (+) showed no inhibitory activity. Four brominated chromans and two tetrahydrobenzo[b]oxepin derivatives also showed apparent inhibition against both cress and oat.

Allelopathy as a new strategy for sustainable ecosystems development

Natural products involved in plant-plant and plant-microorganism ecological interaction (Allelochemicals) are an important potential source for alternative agrochemicals and pharmaceuticals, in order to solve the many problems derived from inadequate culture practices and abuse of synthetic herbicides. Isolation, structural determination, bioassay techniques and applicability for these compounds in crop protection and pharmaceutical research are discussed, and future trends on Allelochemicals applications are examined. The new strategies for sustainable ecosystems controlled by allelochemicals offer a particular interest for the development of human bases in space, since these products can stimulate or inhibit plant germination and growth, and permit to develop crops with low residue amounts in water, facilitating wastewater treatment and recycling.

Palladium-catalyzed sequential alkylation-alkenylation reactions. Application to the synthesis of 2-substituted-4-benzoxepines and 2,5-disubstituted-4-benzoxepines

The synthesis of 2-substituted-4-benzoxepines and 2,5-disubstituted-4-benzoxepines from aryl iodides and bromoenoates is described. This methodology is based on a palladium-catalyzed aromatic substitution followed by an intramolecular Heck sequence. Under the reaction conditions (Pd(OAc)(2) (10 mol %), tri-2-furylphosphine (20 mol %), norbornene (2 equiv), Cs(2)CO(3) (2 equiv), CH(3)CN, 85 degrees C), moderate to excellent yields of benzoxepines bearing numerous substituents (Me, F, Cl, etc.) are obtained.