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The NaBH4 (or TBABH4)-promoted electrochemically reductive cleavage of aryl C-O bonds in diaryl ethers to produce phenols and arenes with high yields and excellent selectivities at room temperature was reported. Air- and water-tolerable, this process also works on the cleavage of aryl alkyl and benzyl ethers. The application to break the β-O-4, α-O-4, and 4-O-5 lignin model compounds is also illustrated, which highlights the advance toward the goal of lignin conversion. [ABSTRACT FROM AUTHOR]

Five new stilbene oligomers, Iaetevirenol A-E (4-8), were isolated from Parthenocissus laetevirens, together with three known stilbene oligomers (2, 3, and 9). The structures of the new compounds were elucidated by spectroscopic analysis, including 1D and 2D NMR experiments. Afterward the absolute configurations were determined. Biomimetic transformations revealed a possible biogenetic route, where stilbene trimers were enzymatically synthesized for the first time. In addition, their antioxidant activities were evaluated by 1,l-diphenyl-2-picrylhydrazyl (DPPH) assay. The results showed that stilbene oligomers with an unusual phenanthrene moiety exhibited much stronger antioxidant activities. Thus, the photocatalyzed cyclization of stilbenes was supposed to be an antioxidant activity promoting transformation, which was hypothesized to play a role in the antioxidative defense system of the plant. [ABSTRACT FROM AUTHOR]

The PdCl2-catalyzed cyclocarbonylation reaction of propargylic amines with CuCl2 and benzoquinone afforded (E)-α-chloroalkylidene-β-lactams in moderate to good yields. The formation of the corresponding Z-isomers or five-membered products was not observed. The reaction of the readily available optically active prop argylic amines provides a convenient synthesis of the corresponding (E)-α-chloroalkylidene-β-lactams with high ee values. The structure and the stereochemistry of the products were established by the X-ray single-crystal diffraction study of (E)-6d and (E)-6e, which indicates that the stereoselectivity in this reaction is different from what was observed with propargylic alcohols. A rationale for this reaction was proposed. [ABSTRACT FROM AUTHOR]

A good regio- and stereoselectivity was observed for the PdCl2-catalyzed cyclocarbonylation of 2-alkynols with CuCl2 affording (Z)-α-chloroalkylidene-β-lactones. The highly optically active (Z)-α-chloroalkylidene-β-lactones could be easily prepared from the readily available optically active prop argylic alcohols. The Pd(II)-catalyzed cyclocarbonylation of 2-alkynols with CuBr2 was also studied. Although the yields of (Z)-α-bromoalkylidene-β-lactones were low, due to the relatively higher activity of the C-Br bond, the coupling reactions of (Z)-α-bromoalkylidene-β-lactones were quite smooth to afford the corresponding products in high yields. A rationale for this reaction is discussed. [ABSTRACT FROM AUTHOR]

4-Halo-5-hydroxyfuran-2(5H)-ones were synthesized via the efficient sequential halolactonization-hydroxylation reaction of 4-aryl-2,3-allenoic acids with I2 or CuX2 (X = Br or Cl) in moderate to good yields. The structures of the products were established by the X-ray single-crystal diffraction study of 3-methyl-4-iodo-5-phenyl-5-hydroxyl2(5H)-furanone (2a). A rationale for this reaction was discussed based on some brief mechanistic study. [ABSTRACT FROM AUTHOR]

Matsutakone (1), a novel sterol with an unprecedented polycyclic ring system, together with a new norsteroid matsutoic acid (2) were isolated from the fruiting bodies of Tricholoma matsutake. Their structures and absolute configurations were assigned by extensive spectroscopic analyses and computational methods. Bioassay results showed that compounds 1 and 2 exhibited inhibitory activities against acetylcholinesterase (IC50 20.9 νM for 1). [ABSTRACT FROM AUTHOR]

H-bonding activation in the regioselective acetylation of vicinal and 1,3-diols is presented. Herein, the acetylation of the hydroxyl group with acetic anhydride can be activated by the formation of H-bonds between the hydroxyl group and anions. The reaction exhibits high regioselectivity when a catalytic amount of tetrabutylammonium acetate is employed. Mechanistic studies indicated that acetate anion forms dual H-bonding complexes with the diol, which facilitates the subsequent regioselective monoacetylation. [ABSTRACT FROM AUTHOR]

Chunganenol (1), an unusual resveratrol hexamer, has been isolated from Vitis chunganensis. Its unprecedented structure has been assigned through detailed analyses of 2D NM R data and consideration of oligostilbene biosynthetic pathway, representing the first highly condensed stilbene oligomer from Vitaceous plants. It also featured a novel interunit Iingkage where two stilbene units are connected by a methylene bridge. Moreover, 1 exhibited potent and selective quenching effects on singlet oxygen, and might play a role in the antioxidative defense system of the plant. [ABSTRACT FROM AUTHOR]

Apoptolidins A-D are microbial secondary metabolites shown to be selectively cytotoxic against several cancer cell lines and noncytotoxic against normal cells. Total syntheses of apoptolidinones A and D are reported. The efficient synthetic strategy leading to the apoptolidinones features construction of the common 20-membered macrolactone by an intramolecular Suzuki reaction and stereocontrolled aldol reactions establishing the C19/C20 and C22/C23 stereocenters. In contrast to apoptolidin A, the aglycones apoptolidinone A and D were shown to be noncytotoxic when evaluated against human lung cancer cells (H292). [ABSTRACT FROM AUTHOR]

Mild, metal-free, highly regioselective hypervalent-iodine mediated C-2 acetoxylation and C-3 oxidations of N-substituted indoles with (diacetoxyiodo)benzene [PhI(OAc)2] have been reported. The reaction involves three cascade steps. The quantity of PhI(OAc)2 employed in this reaction plays a key role in the outcome of three types of products (2a-4a). Furthermore, the mild and highly regioselective C-2 oxidation and C-3 dichlorination of N-substituted indoles with PhICl2 have been developed. Extensive studies including in situ IR techniques and H2O18-labeling experiment were performed to gain insight into the possible reaction mechanism. [ABSTRACT FROM AUTHOR]

An efficient C(sp³)-H bond activation and intramolecular amination reaction via palladium catalysis at the β-position of carboxyamides to make β-lactams was described. The investigation of the substrate scope showed that the current reaction conditions favored activation of the β-methylene group. Short sequences were developed for preparation of various diazabicyclic β-lactam compounds with this method as the key step from chiral proline and piperidine derivatives. [ABSTRACT FROM AUTHOR]

An efficient C(sp³)-H bond activation and intramolecular amination reaction via palladium catalysis at the β-position of carboxyamides to make β-lactams was described. The investigation of the substrate scope showed that the current reaction conditions favored activation of the β-methylene group. Short sequences were developed for preparation of various diazabicyclic β-lactam compounds with this method as the key step from chiral proline and piperidine derivatives. [ABSTRACT FROM AUTHOR]

A novel, highly stereoselective synthesis of an azaspirocyclic core, which contains four stereogenic carbons consistent with structures of natural halichlorine and pinnaic acid, is presented. Lipase PS-catalyzed selective acylation, asymmetric methylation on the α-methylene of the bicyclic lactone, and an asymmetric Michael addition of the tertiary nitro cyclopentane were concisely used to conquer the challenging problem of successfully constructing the C9 quarternary carbon center with complete stereocontrol. The spiropiperidine ring was formed by reduction of the δ-nitroketone, intramolecular condensation, and then highly stereoselective reduction of the cyclic nitrone with NaBH4. This spirocyclic core is a key intermediate in Danishefsky's synthesis of pinnaic acid and halichlorine. [ABSTRACT FROM AUTHOR]