Heteropoly acid catalysts in upgrading of biorenewables: Cycloaddition of aldehydes to monoterpenes in green solvents

Acidic Cs salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40 (CsPW), is excellent solid acid catalyst for liquid-phase cycloaddition reactions of biomass-based and easily available from essential oils monoterpenic compounds, such as limonene, ?-terpineol, ?-pinene, ?-pinene and nerol, with aldehydes, including benzaldehyde, crotonaldehyde as well as biomass-derived cuminaldehyde and trans-cinnamaldehyde. The reactions give oxabicyclo[3.3.1]nonene compounds potentially useful for the fragrance and pharmaceutical industries in good to excellent yields. The process is environmentally benign and can be performed in biomass-derived solvent 2-methyltetrahydrofuran and eco-friendly ?green? organic solvents such as dimethylcarbonate and diethylcarbonate under mild conditions at low catalyst loadings without leaching problems. The solid CsPW catalyst can be easily separated from the reaction media and low-boiling solvents can be removed by distillation. Silica-supported H3PW12O40 also demonstrated good performance in these reactions

Rhodium catalyzed hydroformylation of kaurane derivatives: A route to new diterpenes with potential bioactivity

Kaurenic and grandiflorenic acids are naturally occurring diterpenes whose biological activity has been described. Both acids contain an exocyclic methylenic double bond that allows further functionalization on their structure. In an attempt to expand the number of derivatives of these two natural products, we have undertaken a study on the hydroformylation of the methyl esters of the two acids and the trimethylsilyl ether of kaurenol. These substrates have been hydroformylated by using unmodified Rh catalysts, as well as Rh/PPh3 and Rh/tris-(o-t-butylphenyl)phosphite catalytic systems at 100 °C and 20 bar of CO/H2 (1:1). For the three substrates, the two Rh catalysts modified with P-donor ligands, produced high conversions and chemo- and regioselectivities in the diastereoisomeric pair of linear aldehydes. In all cases, the stereoselectivity observed is strongly dependent of the system used, being the most diastereoselective the least hindered unmodified Rh/CO catalyst. A correlation between the higher diastereoselectivity and the faster [beta]-elimination of the metal-alkyl intermediate observed in the unmodified system is discussed.http://www.sciencedirect.com/science/article/B6TF5-4RVMXFD-3/1/d27e671ad9e0b7fc325dfd0bdf413c7

Organometallic catalysis: some contributions to organic synthesis

In the present paper some general aspects of metal complex catalysis and its applications for oxyfunctionalization of various olefins, including naturally occurring ones, via selective oxidation, hydroformylation and alkoxycarbonylation are discussed

Elucidation of the stereochemistry of diterpene derivatives obtained by palladium catalyzed oxidative coupling-oxidation of camphene

The structures of diterpene derivatives resulting from the palladium catalyzed tandem oxidative coupling-oxidation of camphene, i.e., bis(2,2-dimethyl-bicyclo[2.2.1]hept-3-ylidene)ethane and (4,4-dimethylbicyclo[3.2.1]oct-2-on-3-yl)(2,2-dimethylbicyclo[2.2.1]hept-3-ylidene)methane, were elucidated using one- and two-dimensional ¹H and13C NMR techniques. Their stereochemistry was determined unambiguously by NOESY experiments

Palladium/Heteropoly Acid Catalyzed Oxidative Coupling of 2-Methoxy-1,4-benzoquinone with Arenes

Oxidative coupling of 2-methoxy-1,4-benzoquinone and arenes in acetic acid gives methoxyaryl-substituted 1,4-benzoquinones. The reaction is effectively catalyzed by a Pd(OAc)2/heteropoly acid (H9PMo6V6O40 ) redox system with dioxygen as the final oxidant

An Electrostatically-Anchored Rhodium(I) Catalyst for the Hydroformylation and Tandem Hydroformylation/Acetalization of Biorenewable Allyl Benzenes

A rhodium catalyst anchored in a commercial anion exchange resin (IRA900/TPPMS/Rh) was prepared straightforwardly through a simple protocol from readily available precursors. The material was used as a heterogeneous catalyst for the hydroformylation and tandem sequence hydroformylation/acetalization of eugenol and estragole under mild conditions. The regioselectivity for linear products was ca. 62%, but for the allyl benzenes the branched isomer are also valuable. The performance of the anchored catalyst in hydroformylation was comparable to that of the conventional homogeneous rhodium system; however, its efficiency in the acetalization step was significantly higher. The material can be separated from the reaction solutions by decantation and re-used without a significant loss in activity and selectivity. This simple catalytic method represents an economically attractive route to commercially valuable fragrance compounds starting from the substrates easily available from natural bio-renewable sources