S Limonene oxide

Diastereoselective biohydrolysis of (4S,8/ S)-limonene oxide using whole cells of the strain Aspergillus niger LCP 521 as a biocatalyst, leading to the synthesis of a-bisabolols. 

Further variations on the epoxyketone intermediate theme have been reported. In the first (Scheme 9A) [78], limonene oxide was prepared by Sharpless asymmetric epoxidation of commercial (S)-(-)- perillyl alcohol 65 followed by conversion of the alcohol 66 to the crystalline mesylate, recrystallization to remove stereoisomeric impurities, and reduction with LiAlH4 to give (-)-limonene oxide 59. This was converted to the key epoxyketone 60 by phase transfer catalyzed permanganate oxidation. Control of the trisubstituted alkene stereochemistry was achieved by reaction of the ketone with the anion from (4-methyl-3-pentenyl)diphenylphosphine oxide, yielding the isolable erythro adduct 67, and the trisubstituted E-alkene 52a from spontaneous elimination by the threo adduct. Treatment of the erythro adduct with NaH in DMF resulted... 

Tanabe el al. studied in detail the catalytic action and properties of metal sulfates most of the sulfates showed the maximum acidity and activity by calcination at temperatures below 500°C, with respect to the surface acidity and the acid-catalyzed reaction (118, 119). Other acid-catalyzed reactions were studied with the FeS04 catalyst together with measurement of the surface acidity of the catalyst the substance calcined at 700°C showed the maximum acidity at Ho s 1.5 and proved to be the most active for the polymerization of isobutyl vinyl ether, the isomerization of d-limonene oxide, and the dehydration of 2-propanol (120-122). It is of interest that the catalyst calcined at a slightly higher temperature, 750°C, was completely inactive and zero in acidity in spite of the remarkable activity and acidity when heat treated at 700°C. 

In double stereodifferentiation, the inherent diastereofacial preferences of the chiral reactants may reinforce or oppose one another. Heating (/ )-(+)-limonene with bicyclic oxaziridine (+)-(2/ ,3S)-(105) for 2 days at 60 °C resulted in a 90% yield of a 55 45 cis/trans mixture of limonene oxides (106) (Equation (24)) <91JOC809>. The cis/trans selectivity improved to 93 7 when (S)-(—)-limonene was used. 

Besides pyridine-containing polystyrene and pol)q5ropylene resins, polybenzimidazole has been employed as support for nickel(II) acetylacetonate [94]. The nickel-loaded polymer was shown to be an efficient catalyst for the epoxidation of (S)-(—)-limonene, a-pinene, and 1-octene using isobutyraldehyde/02 as coreac-tant/oxidant. However, significant metal leaching from the support associated with a loss of activity upon recycling was reported. It was shown that the reaction is heterogeneously catalyzed, and leached metal species did not contribute to the catal)d ic activity. 

The unsaturated double bonds in limonene can be epoxidized (11). Carbon dioxide and limonene oxide can be used to get a cyclic limonene dicarbonate. The reaction is shown in Figure 6.4. This compound is useful to produce linear polycarbonates, or poly(ur-ethane)s (PU)s. 

The activity of the FePeCli6-S/tert-butyl hydroperoxide (TBHP) catalytic system was studied under mild reaction conditions for the synthesis of three a,p-unsaturated ketones 2-cyclohexen-l-one, carvone and veibenone by allylic oxidation of cyclohexene, hmonene, and a-pinene, respectively. Substrate conversions were higher than 80% and ketone yields decreased in the following order cyclohexen-1-one (47%), verbenone (22%), and carvone (12%). The large amount of oxidized sites of monoterpenes, especially limonene, may be the reason for the lower ketone yield obtained with this substrate. Additional tests snggested that molecular oxygen can act as co-oxidant and alcohol oxidation is an intermediate step in ketone formation. 

Chiral and achiral Jacobsen s catalysts exhibit similar diatereomeric excesses during the diastereoselective epoxidation of R-(+)-limonene using in situ prepared oxidizing agents. Therefore, the chiral center of the substrate appears to govern the chiral induction. In contrast, the chirality of the Jacobsen s catalyst appears to be responsible for the chiral induction when commercially available oxidants were used. 

The enantioselective synthesis in Scheme 13.22 is based on stereoselective reduction of an a, (3-unsaturated aldehyde generated from (—)-(.V)-limonene (Step A). The reduction was done by Baker s yeast and was completely enantioselective. The diastereoselectivity was not complete, generating an 80 20 mixture, but the diastere-omeric alcohols were purified at this stage. After oxidation to the aldehyde, the remainder of the side chain was introduced by a Grignard addition. The ester function... 

Figure 10.4 Temperature profiles for three classes of analytes monoterpenes (limonene) sesquiterpenes [(3 caryophyllene, caryophyllene oxide (caryo. oxide)] and diterpenes [cem brene A, isoincensole acetate (iso. acetate)]. PDMS fibre, sampling time 40 min. Reproduced from S. Hamm, E. Lesellier, J. Bleton, A. Tchapla, J. Chromatogr., A, 1018, 73 83. Copyright 2003 Elsevier Limited...

The cycloaddition of nitrile oxides RCNO (R = alkyl, alkenyl, aryl), generated in situ from either RCH2NO2/PI1NCO or RCH=NOH/NaOCl to (R)-( + )-limonene, proceeds regioselectively at the extracyclic double bond, but not stereospecifically, to form (5R/S )-isoxazoles 78 in 64% to 81% isolated yield (241). 

E.g. canones, pefdlyl alcohol, limonene fipoxides, verhenonfi, rojir oxj.de, b.nalool oxides, nootkalcm, sdareolide, io iones, irons s... 

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