Butylcyclohexanol, 4-tert

The preparation of cis 4 tert butylcyclohexanol from its trans stereoisomer was earned out by the following sequence of steps Write structural formulas including stereochemistry for com pounds A and B... 

A number of effects of conformation have been reported Crowding of the hydroxyl group results in faster oxidation and alcohols with axial hydroxyl groups are oxidised more readily than the equatorial isomers, e.g. cis-4-tert-butylcyclohexanol is oxidised about three times faster than the trans isomer at 25 °C. 

Sato et al. (1997) have shown that 2-octanol can be converted to 2-octanone, with 95% selectivity, with 3-30% aqueous H2O2 in the presence of a tungsten catalyst and a PTC like trioctylmethylhydrogen sulphate. A similar strategy works for converting A-tert butylcyclohexanol to A-tert butylcyclohexanone. 

The geometry of the cis-alkylcyclohexanol is favorable for trans elimination since the hydroxyl and the neighboring trans hydrogen are coplanar, but this is not true for the l,i-trans isomer hence the molecular conformation has to flip over, to set the hydroxyl group in the axial position for the trans elimination to occur. This would require a few kilocalories of energy and for frans-lert-butylcyclohexanol it would be more difficult to achieve than for IroMs-methylcyclohexanol. It is, therefore, possible that the trans elimination from a boat conformation, or possibly even an epimerization from the trans to the cis isomer which then undergoes a trans elimination reaction. Such an epimerization was found to occur under conditions of dehydration of certain alcohols over alumina, as will be seen under 1,4-cyclohexanediol. The more facile elimination of the cis-i-tert-butylcyclohexanol system as compared with the trans system in solution was also reported in the literature 63). 

The material is prepared by reaction of 2-tert-butylcyclohexanol with sodium hydride and 1,2-epoxy butane [115a]. 

The ester is prepared by catalytic hydrogenation of 4-tert-butylphenol followed by acetylation of the resulting 4-tert-butylcyclohexanol [132]. If Raney nickel is used as the catalyst, a high percentage of the trans isomer is obtained. A rhodium-carbon catalyst yields a high percentage of the cis isomer. The trans alcohol can be isomerized by alkaline catalysts the lower-boiling cis alcohol is then removed continuously from the mixture by distillation [133]. 

It is prepared by esterification of 2-tert-butylcyclohexanol with diethyl carbonate. 

The steric requirements of the surface during the formation of the adsorption complex or transition state also manifest themselves in the dehydration of rigid alcohols with fixed conformations, e.g. of cyclic alcohols. Cis- and trans-2- and 4-alkylcyclohexanols differ markedly in their rate of dehydration on alumina (see Table 5). Most significant are the data on 4-tert-butylcyclohexanols where the bulky ferf-butyl group is in an equatorial position, and thus the differences in the reactivity of the cis and trans isomers indicate the differences in the reactivity of axial and equatorial hydroxyls. The high reactivity of cis-2-terf-butylcyclohex-anol is caused most probably by steric acceleration of the elimination, which is, however, absent in the case of 2,2-dimethylcyclohexanol. 

The compound that reacts with tranx-4-tert-butylcyclohexanol is a sulfonyl chloride and converts the alcohol to the corresponding sulfonate. 

The p anomers of sugars are generally oxidized more rapidly than the a anomers (see later), a similar pattern is seen in the faster oxidation of /1-glycosides. The different rates of oxidation of /1-D-glucopyranosides and their a-D anomers have been attributed to the equatorial orientation of the anomeric hydroxyl group in the 4Ci conformation of the former. Other compounds have shown a similar behavior.10 Thus, the relative rate of oxidation of cw-2-tert-butylcyclohexanol (HO-axial) with respect to the trans isomer (HO-equatorial) is approximately 5 1. 

The important fragrance intermediate 4-tert-butylcyclohexanol 27 (Eq. 15.3.1) is available commercially as an isomer mixture containing about 70% of the preferred c/s-form 27. H. van Bekkum et al.(32) reported on the first stereoselective Meerwein-Ponndorf-Verley reduction (MPV) of 4-tert-butylcyclohexanone to the desired czs-4-tert-butylcyclohexanol catalyzed by zeolite BEA. 

Table 15.4 MPV reduction of 4-tert-butylcyclohexanone with isopropanol to 4-tert- butylcyclohexanol over various heterogeneous catalysts ...

Fig. 15.5 Transition states for the formation of cis- and trans-4-tert-butylcyclohexanol in the proposed reaction mechanism over zeolite BEA...

Bromuhydrin Cyclization 1.0 g (4.2 mmol) of the corresponding bromohydrin [(1 /, 2/ , 35 )-2-bromo-3-tert-butylcyclohexanol or (li , 2R, 6S )-2-bromo-6-terf-butylcyclohexanol, respectively] is dissolved in 20 mL of i-PrOH and titrated using phenolphthalein as indicator. The consumption of base (1 M KOH in EtOH) is 4.2 mL. Dilution with H20, extraction with Et20, drying with MgS04, and evaporation in vacuo gives pure epoxide trans-6 yield 0.6 g (91%) bp 92-94 DC/20 Torr cis-6 yield 0.55 g (83%) bp 82-83 CC/18 Torr. 

A recent example, the stereoselective reduction of 4-tert-butylcyclohexanone to cis-4-tert-butylcyclohexanol with secondary alcohols over zeolite BEA (95% selectivity at 33% conversion)[148] shows however, that not so much the basic character of the molecular... 

Differences in the activity and selectivity for 4-rert-butylphenol hydrogenation are displayed in Fig. 1. The variation in selectivity as a function of conversion shows that cis and trans-4-tert-butylcyclohexanol and 4-terr-butylcyclohexanone are all primary products. It should be noted that... 

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