Oxygenated cyclohexane derivatives

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... 

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 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. 

Oxygen compounds in crude oils are more complex than the sulfur types. However, their presence in petroleum streams is not poisonous to processing catalysts. Many of the oxygen compounds found in crude oils are weakly acidic. They are carboxylic acids, cresylic acid, phenol, and naphthenic acid. Naphthenic acids are mainly cyclopentane and cyclohexane derivatives having a carboxyalkyl side chain. 

In 5-alkyl-substituted 1,3-dioxanes, the 5 substituent has a much smaller preference for the equatorial position than in cyclohexane derivatives the A values are much lower. This indicates that the lone pairs on the oxygens have a smaller steric requirement than the C—H bonds in the corresponding... 

Aldose dithioacetals, which are devoid of leaving groups, notably oxygen-bonded functions at C-2, on treatment with strong bases, afford stable C-l carbanions that allow the formation of cyclohexane derivatives when suitable leaving groups are present at C-6. 

Saturated six-membered heterocyclic rings can be found in various fields of chemistry, e.g., natural products, drugs and polymers. Representative molecules are cyclohexane derivatives in which ring methylenes are either substituted by alkyl or other functional groups or replaced by one or more heteroatoms (mainly nitrogen, oxygen, and sulfur). 

The total synthesis of (+)-cyclophellitol containing a fully oxygenated cyclohexane ring was accomplished by T. Ishikawa and co-workers. The synthetic strategy was based on the intramolecular silyl nitronate [3+2] cycloaddition reaction. The cycloaddition precursor was prepared by the Henry reaction starting from a D-glucose-derived aldehyde. 

The 1,4-elimination of 193, given in the Eqs. 52 and 53, represents two pathways leading to two different iminium ions 194 and 195, whose relative distribution will depend on whether the reaction is performed under thermodynamic or kinetic control. The species 194 is a cyclooctene derivative and the species 195 a cyclohexane derivative. The cyclohexane derivative 195 must, of course, predominate in a thermodynamically controlled reaction. Like the species 193, the species 196 also represents two pathways for 1,4-elimination as shown in Eqs. 54 and 55. Fortunately, both the pathways yield the same product 197. The reactions shown in Eqs. 56 and 57 are examples of elimination resulting from the 1,3-diol mono-tosylate system. An electron pair orbital on the hydroxylic oxygen that is antiperiplanar to the cleaving central ac c bond provides the necessary electronic push in which the former makes the latter weak, and therefore labile for cleavage. The reaction shown in Eq. 57 was used by Corey and coworkers in a synthesis of... 

Although hydroxyl radicals are apparently the active species in oxygenation of benzene [40a], cyclohexane [40a] and even methane [40b] by oxygen-containing derivatives of xenon (which may be generated by dissolution of XeOs or Xep2 in water of aqueous acetonitrile), the mechanism of direct arene epoxidation as the first stage is not excluded [40a] ... 

Of the several reactions available for making cyclohexane derivatives from carbohydrates the present is amongst the most useful. It has been applied in many instances - mainly to the preparation of sugars with a methylene group in place of the ring oxygen atom (carbasugars) and of inositols and inositol derivatives. On occasion, however, it has been used in syntheses related to natural compounds outside these areas [7]. 

Oxidation of Methyl-substituted Cyclohexane. Methyltrioxorhenium is a versatile catalyst for the oxidative functionalization of cyclohexane derivatives with H2O2 as oxygen donor. Interestingly, there is a difference between the two stereoisomeric cis- and frans -configurations (eqs 47 and 48). ... 

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