Terpenes, allylic oxidation

Oxygenated monoterpenes which are found in almost every bark beetle species attacking coniferous trees, include czs-verbenol 246, frans-verbenol 247, and myrtenol 248, representing primary products of allylic oxidation of the host terpene a-pinene 45. Further oxidation of 247 or 248 leads to the... 

Using the most active catalyst (CoNaY) we have studied the oxidation of olefins of different structure and size of molecules, including a number of natural terpenes, namely, (+)-a-pinene (1), (+)-3-carene (2), (-)-caryophyllene (3) and dipentene (4). We have found that even acid-sensitive epoxides that are known to be prone to ring cleavage (caryophyllene epoxide, for example) can be obtained with high-to-exceUent selectivity (Table 2). It is noteworthy that neither allylic oxidation nor overoxidation occurs in the systems studied. Diolefins give mono-... 

Soluble chromium compounds are known to catalyze the allylic oxidation of olefins [22,23] and benzylic oxidations of alkyl aromatics [22,24] using tert-butyl-hydroperoxide as the primary oxidant. Chromium-substituted aluminophosphates, e. g. CrAPO-5, were shown to catalyze the allylic oxidation of a variety of terpene substrates with TBHP to give the corresponding enones [25,26]. For example, a-pinene afforded verbenone with 77% selectivity (Eq. 6) and 13% of the corresponding alcohol. 

POMs can he immobilized onto anion-exchange resins and surface-modified metal oxides with quaternary ammonium cation- or amino-functional groups via anion-exchange. Jacobs and coworkers tethered Venturello s catalyst [P04(W0(02)2)4]3-on a commercially available nitrate-form resin with alkylammonium cations and have carried out the epoxidation of allylic alcohols and terpenes with this supported catalyst [166, 167]. The regio- and diastereoselectivity of the parent homogeneous catalysts were preserved in the supported catalyst. For bulky alkenes, the reactivity of the POM catalyst was superior to that of Ti- 3 zeolite with a large pore size. The catalytic activity of the recycled catalyst was maintained completely after several cycles. 

As an example of carbometallation, the 1,4-carbosilylation product 218 is obtained by the reaction of dienes, disilanes and acid chlorides of aromatic and a,/i-unsaturatcd acids at 80 °C. The phenylpalladium 216 is formed by the oxidative addition of benzoyl chloride, followed by facile decarbonylation at 80 °C, and reacts with butadiene to generate the benzyl-7i-allylic complex 217. Then, transmetallation with the disilane and reductive elimination afford 4-silyl-2-butenylbenzene 218 [92], Regioselective carbomagnesation of isoprene with allylic magnesium bromide 219 catalysed by Cp2TiCl2 gives 220, which is useful for terpene synthesis [93,94],... 

A terpene-derived pyridine N-oxide catalyses the asymmetric allylation of aldehy- des with allyl- and crotyl-trichlorosilane at —40 C, and the ees hold up well even at ambient temperature.189... 

Oxidation of tetraterpenes yields many compounds, and the cyclic compounds with a trimethylcyclohexane ring are easily associated with degradation of monocyclic and bicyclic carotenes, but allylic compounds are now as conspicuous in their biogenetlc origin. Many such compounds are derived from lycopene, phytoene and phyto-fluene, three very common acyclic carotenes. These allylic compounds are often identified only as terpene aldehydes and ketones and not as carotene degradation products (10). 

Key Words Ethylene oxide, Propylene oxide. Epoxybutene, Market, Isoamylene oxide. Cyclohexene oxide. Styrene oxide, Norbornene oxide. Epichlorohydrin, Epoxy resins, Carbamazepine, Terpenes, Limonene, a-Pinene, Fatty acid epoxides, Allyl epoxides, Sharpless epoxidation. Turnover frequency, Space time yield. Hydrogen peroxide, Polyoxometallates, Phase-transfer reagents, Methyltrioxorhenium (MTO), Fluorinated acetone, Alkylmetaborate esters. Alumina, Iminium salts, Porphyrins, Jacobsen-Katsuki oxidation, Salen, Peroxoacetic acid, P450 BM-3, Escherichia coli, lodosylbenzene, Oxometallacycle, DFT, Lewis acid mechanism, Metalladioxolane, Mimoun complex, Sheldon complex, Michaelis-Menten, Schiff bases. Redox mechanism. Oxygen-rebound mechanism, Spiro structure. 2008 Elsevier B.V. 

The polymerization is said to be fast with a low energy input, is not inhibited by air, uses no solvents, is nonpolluting, and uses inexpensive materials. The photopolymerization of various epoxidized oils and terpenes also does this. The propenyl ethers were made by isomerization of the corresponding allyl ethers with a ruthenium catalyst. The allyl ethers were made from the hydroxy compounds with allyl bromide and base, a process that produces waste salts. It is possible that the monomers could be made by reaction of the hydroxy compounds with propylene oxide followed by dehydration so that no waste salts would be formed. Isosorbide is made by the acid-catalyzed dehydration of sorbitol, in turn, obtained by the reduction of glucose. 

Palladium-catalyzed allylic acetoxylation has also been applied to terpene substrates [17], e. g. (/ )-limonene (Eq. 2), albeit using stoichiometric amounts of Cu(II) or benzoquinone as the oxidant. 

Before the modern era of organotransition metal reactivity, it was observed that nickel carbonyl reacted with 2-methallyl chloride in methanol to give methyl 3-methyl-3-butenoate and 2,5-dimethyl-l,5-hexadiene as a by-product. In THF at 25 °C, the diene was the exclusive product. This mild formation of a carbon-carbon bond, and the interest in the synthesis of terpene-based natural products led to efforts to test the scope and limitations of the process. An obvious pathway involves stepwise oxidative addition of each allyl unit followed by Reductive Elimination. As discussed below, the key intermediates (left vague in Scheme 48) are likely to involve Ni -NP couples. 

Terpene-derived bis-N-oxide 21.22 represent the most recent addition to the successful catalyst series. The catalyst was shown to be particularly efficient in the allylation and crotylation of aromatic and a,p-unsaturated aldehydes (<99% enantiomeric excess at —60°C), however, with aliphatic aldehydes the selectivity dropped to 50% ee. It is noteworthy that 21.22 was synthesised in four easy steps from inexpensive (I )-myrtenal and the protocol is amendable to scaling up. In contrast, synthesis of enantiopure catalysts 21.19-21.21 requires either resolution of enantiomers or separation of diastereoisomeric mixtures, which hampers their larger-scale application. In this group of polydentate IV-oxides it is also worth mentioning terpyridine N,IV IV"-trioxide, the related bis-imidazole Af,M -dioxides and chiral dinitrones,but their efficiency was inferior to the best pyridine-type dioxides, such as 21.20-21.22. 

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