Highly Oxygenated Cyclohexanes

The highly oxygenated cyclohexane derivatives listed in Table 6.2.6 were found in several plants belonging to different orders Magnoliales, Geraniales, and Piper-ales. Some of them are constituents of fruits or leaves. 

In 1968, Holland et al. isolated senepoxide (90) and related seneol (91) from Uvaria catocarpa (Annonaceae, Magnoliales) (51). The fruit of this plant, so-called senasena in Madagascar, has been used as a medicine, particularly for children. 

However, the biological activity of these two compounds was not examined in their report (51). 

Pipoxide (93) was found in R hookeri (118) as well as in Uvaria purpurea (50). The structure of pipoxide was determined to be (93) by NMR spectroscopy and by X-ray crystallography (50). 

These compounds are not aromatic, because the aromatic ring has been oxidized to an epoxide (67). The biogenesis of these cyclohexane-epoxides remains to be solved, although hypothetical pathways involving an arene oxide have been proposed (43, 57). 

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Diels-AUer reactions. This diene can serve as a precursor to the highly oxygenated cyclohexane derivative shikimic acid (3), as shown in Scheme 1. Oxidative desilylation of the Diels-Alder adduct 2 could not be effected with peracids, but was effected by cis-dihydroxylation (Upjohn procedure, 7, 256-257) followed by p-elimination of (CH3)3SiOH with TsOH. Introduction of the 4a,5P diol system was effected indirectly from the 4a,5a-epoxide in several steps, since direct hydrolysis of the epoxide resulted in a mixture of three triols.1... 

The first total synthesis of cyclophelitol was achieved by Tatsuta s group in 1990 [11]. The key point of their synthetic strategy is the construction of this highly oxygenated cyclohexane via intramolecular [3+2] cycloaddition of a nitrile oxide to an alkene. 

Beside the retro Diels-Alder procedure, we have extensively applied intermolecular and intramolecular Diels-Alder reaction for natural products synthesis. Palitantin (44), one of the highly oxygenated cyclohexane derivatives, was isolated from Pemcillium... 

An interesting approach to the synthesis of highly oxygenated cyclohexane derivatives has been developed by Ichihara. Benzoquinone epoxides and epox-ycyclohexenones were obtained by the thermal retro Diels-Alder reaction of epoxide 511, obtained from quinones and dimethylfulvene without isolation of the primary adduct. Intermediate 512 (R = Ac), obtained in this way from hydroxymethyl-benzoquinone, was converted into the natural compound sene-poxide (514) as shown in Scheme 6. Reductive, regioselective cleavage of the diepoxide 513 was achieved by treatment with hydrazine hydrate. The stereoselective total synthesis of crotoepoxide (515) from cyclohexenone 512 (R = Ms), and of other natural compounds with related structure, was described. ... 

The highly oxygenated sesquiterpene paniculide A was synthesized by N. Chida et al. starting from D-glucose. The key step to construct the substituted cyclohexane subunit of the natural product involved the Type II Ferrier rearrangement. 

A Nudepore membrane is characterised with perraporometry using cyclohexane as condensable vapour. At a relative pressure of 0.78 a high oxygen flux can be observed which does not increase further upon decreasing the relative vapour pressure. The t-layer of cyclohexane in the pore is 0.5 nm. The expraiment is performed at 34 C. 

High Peroxide Process. An alternative to maximizing selectivity to KA in the cyclohexane oxidation step is a process which seeks to maximize cyclohexyUiydroperoxide, also called P or CHHP. This peroxide is one of the first intermediates produced in the oxidation of cyclohexane. It is produced when a cyclohexyl radical reacts with an oxygen molecule (78) to form the cyclohexyUiydroperoxy radical. This radical can extract a hydrogen atom from a cyclohexane molecule, to produce CHHP and another cyclohexyl radical, which extends the free-radical reaction chain. 

Concern for the conservation of energy and materials maintains high interest in catalytic and electrochemistry. Oxygen in the presence of metal catalysts is used in CUPROUS ION-CATALYZED OXIDATIVE CLEAVAGE OF AROMATIC o-DIAMINES BY OXYGEN (E,Z)-2,4-HEXADIENEDINITRILE and OXIDATION WITH BIS(SALI-CYLIDENE)ETHYLENEDIIMINOCOBALT(II) (SALCOMINE) 2,6-DI-important industrial method, is accomplished in a convenient lab-scale process in ALDEHYDES FROM OLEFINS CYCLOHEXANE-CARBOXALDEHYDE. An effective and useful electrochemical synthesis is illustrated in the procedure 3,3,6,6-TETRAMETHOXY-1,4-CYCLOHEX ADIENE. ... 

Thus, it was shown that Co-Si-TUD-1 is a highly active catalyst for the oxidation of cyclohexane, has a high selectivity for mono-oxygenated species and cyclohexanone, and can be used repeatedly. 

Certain false positives are common (EPA 8020). For example, trimethylben-zenes and gasoline constituents are freqnently identified as chlorobenzenes (EPA 602, EPA 8020) becanse these componnds elnte with nearly the same retention times from nonpolar columns. Cyclohexane is often mistaken for benzene (EPA 8015/8020) becanse both compounds are detected by a 10.2-eV photoionization detector and have nearly the same elntion time from a nonpolar colnmn (EPA 8015). The two compounds have very different retention times on a more polar column (EPA 8020), but a more polar column skews the carbon ranges (EPA 8015). False positives for oxygenates in gasoline are common, especially in highly contaminated samples. 

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