Palladium-catalyzed electrophilic substitution of allyl chlorides and acetates via bis-allylpalladium intermediates

Palladium-catalyzed electrophilic allylic substitution of functionalized allyl chlorides and allyl acetates can be achieved in the presence of hexamethylditin under mild and neutral reaction conditions. This efficient one-pot procedure involves palladium-catalyzed formation of transient allylstannanes followed by generation of a bis-allylpalladium intermediate, which subsequently reacts with electrophiles. Using this catalytic transformation, various aldehydes and imines can be allylated providing highly functionalized homoallyl alcohols and amines. Furthermore, tandem bis-allylation reactions could be performed by employing tosyl isocyanate and benzylidenemalonitrile as substrates. A particularly interesting mechanistic feature of this reaction is that palladium catalyzes up to three different transformations in each catalytic cycle. Various allylic functionalities, including COOEt, CONH(2), COCH(3), CN, Ph, and CH(3), are tolerated in the catalytic reactions due to the application of neutral and mild reaction conditions. The substitution reaction occurs with very high regioselectivity at the branched allylic terminus. Moreover, in several reactions, a high stereoselectivity was observed indicating that this new catalytic process has a high potential for stereoselective synthesis. The regioselectivity of the reaction can be explained on the basis of DFT calculations. These studies indicate that the allylic substituent prefers the gamma-position of the eta(1)-allyl moiety of the reaction intermediate.     

Trichilianones A-D,Novel Cyclopropane-Type Limonoids from Trichilia adolfi

The fractionation of an ethanol extract of the bark of Trichilia adolfi yielded four novel limonoids (trichilinones A-D, 1–4), with five fused rings and related to the hortiolide-type limonoids. Starting with an ε-lactone, which is α,β-unsaturated in trichilinones A and D (1 and 4), attached to a tetrahydrofuran ring that is connected to an unusual bicyclo [5.1.0] hexane system, joined with a cyclopentanone with a 3-furanyl substituent [(2-oxo)-furan-(5H)-3-yl in trichilinone D (4)], the four compounds isolated display a new 7/5/3/5/5 limonoid ring system. Their structures were established based on extensive analysis of NMR spectroscopic data. As the crude extract possessed anti-leishmanial properties, the compounds were assayed for cytotoxic and anti-parasitic activities in vitro in murine macrophages cells (Raw 264.7) and leishmania promastigotes (L. amazoniensis and L. braziliensis), respectively. The compounds showed moderate cytotoxicity (approximately 70 μg/mL), but are not responsible for the leishmanicidal effect of the extract.     

Diterpenoids from Coprinus heptemerus

Seven diterpenoids, isolated due to their ability to inhibit spore germination in the plant pathogenic fungus Magnaporthe grisea, were obtained from cultures of the basidiomycete Coprinus heptemerus. The structures of the compounds, named heptemerones A-G, were determined with spectroscopic techniques.     

Antioxidant secondary metabolites from Geranium lasiopus Boiss. & Heldr

Chromatographic studies on the EtOAc soluble portion of the MeOH extract of Geranium lasiopus led to the isolation of eight flavonoids (kaempferol (1), quercetin (2), quercetin 3-O-β-glucopyranoside (3), quercetin 3-O-β-galactopyranoside (4), kaempferol 3-O-α-rhamnopyranosyl-(1?→?6)-β-glucopyranoside (5), quercetin 3-O-α-rhamnopyranosyl-(1?→?6)-β-glucopyranoside (6), kaempferol 3-O-α-rhamnopyranosyl-(1?→?2)-β-glucopyranoside (7) and quercetin 3-O-α-rhamnopyranosyl-(1?→?2)-β-glucopyranoside (8)), two simple phenolic compounds (gallic acid (9) and its methyl ester (10)) and a hydrolysable tannin (pusilagin (11)). The structures of the compounds were elucidated by 1- and 2-dimensional NMR techniques ((1)H, (13)C, COSY, HMBC, HMQC) and ESI-TOF-MS spectrometry. Inhibitory effects on H(2)O(2)-induced lipid peroxidation in human red blood cells of the different extracts of G. lasiopus, as well as isolated compounds, were investigated. All tested compounds showed comparable or higher activity than that of ascorbic acid and trolox.     

New sesquiterpenes in a proposed russulaceae chemical defense system

In addition to already known sesquiterpene aldehydes, the lactaranes piperdial 1 and piperalol 2 were isolated from extracts of $\text{Lactarius piperatus}$, $\text{L. torminosus}$ and $\text{Russula queletii}$ (larger fungi).     

Palladium-catalyzed coupling of allyl acetates with aldehyde and imine electrophiles in the presence of Bis(pinacolato)diboron

[reaction: see text] An efficient one-pot procedure was developed for palladium-catalyzed electrophilic substitution of allyl acetates (2a-h) in the presence of bis(pinacolato)diboron (1). These reactions proceed with an excellent regioselectivity and with a remarkably high stereoselectivity. The catalytic transformations take place via palladium-catalyzed formation of allyl boronates, which subsequently react with aldehyde (3) and sulfon-imine (4) electrophiles to afford homoallylic alcohols (5a-h) and amines (6a-d), respectively. A particularly interesting mechanistic feature is that the allylic substitution of the transient allyl boronate with sulfon-imine requires palladium catalysis. This finding indicates that the formation of the homoallylic amine derivatives (6a-d) involves bis-allylpalladium intermediates.     

Palladium pincer-complex catalyzed allylation of tosylimines by potassium trifluoro(allyl)borates

Palladium pincer complex 1 catalyzes the reaction of trifluoro(allyl)borate 2 with a wide range of tosylimines (3) under mild and neutral reaction conditions. This catalytic transformation affords homoallylic amines (4) in good to excellent yield. Mechanistic studies suggest that a transmetalation reaction between complex 1 and the borate salt 2 provides an eta(1)-allylpalladium complex, which subsequently reacts with the imine substrate. [Reaction: see text]