Regiodivergent Halogenation of Vinylogous Esters: One-Pot, Transition-Metal-Free Access to Differentiated Haloresorcinols

Asymmetric Total Syntheses of ent-Stachybotrin C and Its Congener

The asymmetric total syntheses of ent-stachybotrin C and its congener have been accomplished through a convergent approach in the longest linear sequence of 12 steps from commercially available materials, respectively. Noteworthy transformation of the synthesis involved a cascade Knoevenagel condensation/Hantzsch ester reduction/epoxide ring-opening/transetherification to construct the core pyran ring with two adjacent stereocenters.

Iron-Catalyzed Gamma-Gamma Dimerization of Siloxydienes

We report the oxidative dimerization reaction of siloxydienes derived from simple enones that creates a new gamma-gamma (γ-γ) C-C bond using catalytic iron and benzoyl peroxide as the terminal oxidant in acetonitrile solvent at ambient temperature. The reaction shows a broad substrate scope including cyclic and acyclic siloxydienes derived from ketones, aldehydes, and esters, which are converted to 1,8-dicarbonyl compounds under mild catalytic reaction conditions in 19-89 % yield across 30 examples. The method is suitable for the coupling of sterically demanding carbon centers, including the formation of vicinal quaternary centers. Conceptually, the dienol ether serves as a precursor to a conjugated radical cation, which undergoes highly site selective γ-dimerization reactions. The γ-γ dimerization strategy is applied to the synthesis of a bioactive analogue of honokiol.

Different Performances of BF3, BCl3, and BBr3 in Hypervalent Iodine-Catalyzed Halogenations

Herein, hypervalent iodine-catalyzed halogenation of aryl-activated alkenes using BX₃ (X = Cl, Br) as the halogen source and activating reagents was reported. Various halogenated 1,3-oxazine/2-oxazoline derivatives were obtained in good-to-high yields. Using BF₃ resulted in different substitute sites from BBr₃ and BCl₃ of the products, indicating different reactive intermediates and reaction pathways. The reaction underwent a "ligand coupling/oxidative addition/intermolecular nucleophilic attack/1,2-aryl migration/reductive elimination/intramolecular nucleophilic attack" cascade when BF₃ was applied as the halogen source, while 1,2-aryl migration has "disappeared" when the halogen source was BBr₃ or BCl₃. Possible catalytic cycles were proposed, and DFT calculations were conducted to demonstrate the differences among BX₃ (X = F, Cl, Br) in the hypervalent iodine-catalyzed halogenations.

Palladium-Catalyzed Direct γ-C(sp3)-H Arylation of β-Alkoxy Cyclohexenones: Reaction Scope and Mechanistic Insights

Direct γ-C(sp3)-arylation of unactivated electron-rich enones is a long-standing challenge. Herein, we report a mild Pd-catalyzed method for direct γ-C(sp3)-arylation of various unactivated β-alkoxy cyclohexenones. The method is not only...

Total Synthesis of (±) Commiphoranes C-D and their Epimers

(±) Commiphorane C, (±) commiphorane D, and their two isomers were synthesized through a linear synthesis strategy in 14 steps. Key features of the strategy include the construction of the...

Formation of 3-Aminophenols from Cyclohexane-1,3-diones

meta-Aminophenols are formed by the action of DBU on 3-amino-2-chlorocyclohex-2-en-1-ones at room temperature in MeCN. The chloro compounds are generated by treating 3-aminocyclohex-2-en-1-ones with the easily prepared halogenating agent BnNMe₃·ICl₂ in MeOH-CH₂Cl₂. The amino group must carry two substituents, either two aryl, one aryl and one alkyl, or two alkyl groups; 3-aminocyclohex-2-en-1-ones of this type are readily made from cyclohex-2-en-1-one and a primary or secondary amine.

Catalytic dehydrogenative aromatization of cyclohexanones and cyclohexenones

Prompted by the scant attention paid by published literature reviews to the comprehensive catalytic dehydrogenative aromatization of cyclohexa(e)nones, this review describes recent methods developed to-date involving transition-metal-catalyzed oxidative aromatization and metal-free strategies for the transformation of cyclohexa(e)nones to substituted phenols.

Total Synthesis of Grifolin, Grifolic Acid, LL-Z1272α, LL-Z1272β, and Ilicicolinic Acid A

A novel synthetic approach for the synthesis of bioactive phenolic natural products is reported. This strategy highlights the power of halogenative aromatization reactions recently developed in our group for preparing densely functionalized arenes in a controlled fashion. Five natural products related by an aromatic core and a farnesyl side chain are synthesized. In contrast to prior methods, this synthesis features high efficiency and generality that permits preparation of targets in gram-scale quantities.

Copper-Catalyzed γ-Sulfonylation of α,β-Unsaturated Carbonyl Compounds by Means of Silyl Dienol Ethers

A regioselective method for the introduction of sulfonyl groups at the γ-carbon of enone systems is reported. Using a copper catalyst and readily available sulfonyl chlorides, a range of silyl dienol ethers are sulfonylated in good yield under mild reaction conditions. The sulfone derivatives formed are poised for further synthetic manipulations as demonstrated by regioselective alkylations.