6-Methyl-2-cyclohexenol

The microbial oxidation of 1-methylcyclohexene (10) with Aspergillus niger gives ( + )-2-methyI-2-cyclohexenol (11), 2-methyl-2-cyclohexen-6-one (12), and the hydration product, 1-mcthylcy-clohexanol (13), while 4-methylcyclohexene (14) affords rac-6-methyl-2-cyclohexenol (15) and the corresponding ketone (16)361-362. 

Complete enantiomer discrimination and asymmetric deactivation of the racemic XylBINAP-RuCl2(dmf) ( )-7b using DM-DABN as a chiral poison are shown to be effective in the kinetic resolution of 2-cyclohexenol (Scheme 8.9). Use of just a 0.5 molar amount of (5)-DM-DABN relative to ( )-7b gives enantiopure (S)-2-cyclohexenol, which is kinetically resolved in the same conversion as enantiopure 7b. Indeed, the relative rate of hydrogenation of (R)- versus (5)-2-cyclohexenol in the presence of only a 0.5 molar amount of (5)-DM-DABN relative to ( )-7b is significantly large (kf/kg = 102). The combination of ( )-7b with (S)-DM-DABN also gives 99.3% ee of (R)-methyl 3-hydroxybutanoate quantitatively... 

When racemic 3-methyl-2-cyclohexenol is hydrogenated by the BINAP-Ru catalyst at 4 atm H2, trcms- and cis-3-methylcyclohexanol are produced in a 300 1 ratio (Scheme 33). The reaction with the (/ )-BINAP complex affords the saturated R,3R trans alcohol in 95% ee in 46% yield and unreacted S allylic alcohol in 80% ee with 54% recovery. 

Recently two heterogeneous TPAP-catalysts were developed, which could be recycled successfully and displayed no leaching In the first example the tetra-alkylammonium perruthenate was tethered to the internal surface of mesopor-ous silica (MCM-41) and was shown [153] to catalyze the selective aerobic oxidation of primary and secondary allylic and benzylic alcohols. Surprisingly, both cyclohexanol and cyclohexenol were unreactive although these substrates can easily be accommodated in the pores of MCM-41. The second example involves straightforward doping of methyl modified silica, denoted as ormosil, with tetra-propylammonium perruthenate via the sol-gel process [154]. A serious disadvantage of this system is the low-turnover frequency (1.0 and 1.8 h-1) observed for primary aliphatic alcohol and allylic alcohol respectively. 

Another example of this type of substrate-induced diastereoselectivity is represented by the rearrangement of the S -methyl xanthate of cis-3,5-dimethyl-2-cyclohexenol 5, which takes place on heating at 140 °C for a few hours, to give 644. 

When t7. -l-(2,5-dichlorophenyl)-4-methyl-2-cyclohexenol is treated with 2,4-dinitrobenzene-sulfenyl chloride in the presence of triethylamine. the allylic sulfoxide 9 is stereoselectively formed via [2,3] sigmatropic rearrangement of the initially formed sulfenate ester 8106. 

In the addition reaction of phenylselenenyl chloride to 2-cyclohexenol a single diastereomer 7 A is produced, while 5-methyl-2-cyclohexenol gives a mixture of two regioisomers 7B and 8 in a 7 3 ratio24. 

Geraniol or nerol can be converted to citronellol in 96-99% ee in quantitative yield without saturation of the C(6)-C(7) double bond (eq 6). The S C ratio approaches 50000. The use of alcoholic solvents such as methanol or ethanol and initial H2 pressure greater than 30 atm is required to obtain high enantioselectivity. Diastereoselective hydrogenation of the enantiomerically pure al-lylic alcohol with an azetidinone skeleton proceeds at atmospheric pressure in the presence of an (i )-BINAP-Ru complex to afford the (3-methyl product, a precursor of ip-methylcarbapenem antibiotics (eq 7). Racemic allylic alcohols such as 3-methyl-2-cyclohexenol and 4-hydroxy-2-cyclopentenone can be effectively resolved by the BINAP-Ru-catalyzed hydrogenation (eq 8). ... 

Cyclohexenol, trans-5-methyl 30-2° 0095m HCIO4 (35% aq. acetone)... 

The isotopic exchange reactions between a secondary alcohol and water were further investigated by Goering and Josephson (1962) in connection with the oxygen exchange accompanying the acid-catalysed allylic rearrangement of cis- (7) and fraws-5-methyl-2-cyclohexenol (8) in aqueous acetone. 

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