Borneol oxidation

Borneol oxidation to camphor, new procedure Sonogashira Coupling of lodoaromatic Compounds with Alkynes... 

Borneol and isoboineol are respectively the endo and exo forms of the alcohol. Borneol can be prepared by reduction of camphor inactive borneol is also obtained by the acid hydration of pinene or camphene. Borneol has a smell like camphor. The m.p. of the optically active forms is 208-5 C but the racemic form has m.p. 210-5 C. Oxidized to camphor, dehydrated to camphene. 

The structure of the bicychc monoterpene borneol is shown in Figure 26 7 Isoborneol a stereoisomer of borneol can be prepared in the labora tory by a two step sequence In the first step borneol is oxidized to camphor by treatment with chromic acid In the second step camphor is reduced with sodium borohydride to a mixture of 85% isoborneol and 15% borneol On the basis of these transformations deduce structural formulas for isoborneol and camphor... 

Thin-Layer Chromatography TLC) The function of TLC in organic synthesis is primarily one of allowing the experimenter to follow the progress of the reaction without actually interrupting the reaction. Since successful TLC can be carried out on a minute scale, only a very small fraction of the reaction mixture need be withdrawn and subjected to analysis. The following example of the TLC analysis of the chromic acid oxidation of borneol, described by Davis (3), is a useful model. 

One milliliter each of the borneol solution and the oxidizing solution are mixed in a test tube and briefly shaken. A TLC slide is spotted with the borneol solution, the camphor solution, and the ether layer of the reaction mixture. Spotting is done by means of a capillary melting point tube used as a dropper and filled with a 5 mm sample. The slide is developed in a wide-mouth jar containing a filter paper liner and a few milliliters of chloroform (Fig. A3.20). After development (the solvent front rises to within 1 cm of the top), the slide is removed, the solvent is allowed to evaporate, and the slide is placed in a covered wide-mouth jar containing a few crystals of iodine. The spots readily become visible and the progress of the reaction can easily be followed. With periodic shaking, the oxidation is complete in about 30 minutes. 

Isoborneol yields camphor on oxidation, but it yields camphene on dehydration much more readily than borneol does. If a solution of isoborneol in benzene be heated with chloride of zinc for an hour, an almost quantitative yield of camphene is obtained. Pure borneol under the same conditions is practically unchanged. 

Camphor, Cj HjgO, occurs in the wood of the camphor tree Laurus camphora) as dextro-camphor. This is the ordinary camphor of commerce, known as Japan camphor, whilst the less common laevo-camphor is found in the oil of Matricaria parthenium. Camphor can also be obtained by the oxidation of borneol or isoborneol with nitric acid. Camphor may be prepared from turpentine in numerous ways, and there are many patents existing for its artificial preparation. Artificial camphor, however, does not appear to be able to compete commercially with the natural product. Amongst the methods may be enumerated the following —... 

Because both enantiomers, (+) and (-)-camphoric add, are available by oxidation either from natural (+)-D-camphor or from natural (-)-L-borneol, both enantiomers of camphanoyl chloride can be prepared conveniently.3 5 The corresponding enantiomers of camphanic acid were described for the first time by Wreden6and Aschan.7 The three-step procedure, described above is an adaptation of procedures described by Aschan,8 Zelinsky et al.,9 Meyer et al.,10 and Gerlach.3... 

Alcohols with ring strain can be oxidized by the direct method. Borneol (7) was electrochemically oxidized in MeOH with cleavage of the Ca Cp bond to afford (8) with an endojexo ratio of 97/3 in more than 70% yield at 5 F mol (Scheme 2) [11]. 

N-Hydroxyphthalimide A-Hydroxyphth-alimide (NHPI) was shown to be a mediator for the electrochemical oxidation of (1) to (2) (Eq. 6) [57, 58], although the yields of (2) were not always satisfactory. A large deuterium isotope effect ( h/ d = 10.6) was observed in the oxidation of benzhydrol [59]. Recently, tetrafluoro-NHPI was found to be efficient for the oxidation of borneol [60]. 

SCHEME 122. Selective oxidation of borneols and menthols with immobilized Mo catalysts and TBHP... 

A slightly modified procedure - oxidation with 100 per cent excess of chromic acid at 0 °C for a short period - is adopted for strained bicyclic alcohols (e.g. the oxidation of ( —)-borneol to ( —)-camphor, Expt 5.87) and gives excellent yields of the corresponding ketones. Cycle ketones which are susceptible to acid-catalysed epimerisation are moreover obtained by this procedure in a high degree of epimeric purity. 

The most straightforward method involves the conversion of pinene [l] into pinene hydrochloride [2], bornylchloride [3] and hence into borneol [6] (or iso-borneol) from which camphor [7] is obtained by oxidation. Also bornylchloride [3] is converted to isobro-nylacetate [5] upon heating with sodium acetate and glacial acetic acid. Alternatively, c-amphene [U] is oxidatively hydrated to camphor [7]-... 

Interestingly, both endo- and exo-borneol are oxidized to camphor at the same rate, despite the enormous difference in the steric environment of these two alcohols (Table V, Entries 9 and 10). 

Unless otherwise stated, all the conversions are quantitative. rfThe oxidation was performed on a 80/20 mixture of borneol and iso-borneol. The oxidation was effected on a 30/70 mixture of axial and equatorial isomers. The conversion amounted to 95% in this case. 

The first enantioasymmetric polymerisation of (R, propylene oxide, reported in 1962, was carried out in the presence of the diethylzinc (+)-borneol catalyst [23,24]. Other optically active catalysts for propylene oxide stereoelective polymerisation, e.g. diethylzinc (R)-( )-3,3-dimethyl-1,2-butanediol were described later on [25]. 

Borneol, chiral auxiliary in nitrile oxide cycloadditions, 60, 287-8 Borole, calculations, resonance energies, 56, 364... 

The cycloaddition reaction of chiral thiocarbonyl 5-oxides derived from terpene alcohols such as (—)-menthol, ( —)-borneol, (+)-a-fenchol and (—)-3-tWo-hydroxy-2-CTitfo-phenylbornane affords 2-substituted 2-alkoxysulfonyl-3,6-dihydro-4,5-dimethyl-2//-thiopyran 1-oxides IIA and 11B as a mixture of diastereomers85. 

Bicyclic cyclopropyl compounds are anodically dimethoxylated to give stereoisomeric cis and trans) cyclopropane ring-opened products, as in Eq. (48) [322]. Shono and coworkers [323] reported a different type of ring-opening reaction of a cyclobutyl compound through anodic methoxylation. They also found that anodic oxidation of borneol and isoborneol in methanol resulted in a rearrangement to provide methoxylated stereoisomeric products with the same endo-exo ratio, as in Eq. (49) [324] ... 

When borneol (ROH) is fed to a dog, this toxic substance is excreted as compound P, QHgOe—OR, where R stands for the bornyl group. Compound P does not reduce Benedict s solution. It reacts with aqueous NaHC03 with the liberation of a gas. Treatment of P with aqueous acid yields borneol (ROH) and D-glucuronic acid (Table 34.1), which is oxidized by bromine water to D-glucaric acid. 

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