SOLVOMERCURATION-DEMERCURATION .7. REGIOCHEMISTRY AND STEREOCHEMISTRY OF THE OXYMERCURATION-DEMERCURATION OF ALKYL-SUBSTITUTED CYCLOHEXENES AND CYCLOPENTENES

The oxymercuration-demercuration (OM-DM) of several methyl-and tert-butylcyclohexenes and cyclopentenes has been investigated. The conformationally flexible 4-methylcyclohexene undergoes hydration in a nonregioselective but remarkably stereoselective fashion, giving a 50: 50 ratio of the trans-3-and cis-4-methylcyclohexa-nols with only ~1% each of the other two isomers. In the case of 3-methylcyclohexene, hydration occurs both regio-and stereoselectively to give 79% trans-3-, 12% cis-2-, 5% cis-3-, and 4% trans-2-methylcyclohexanols. A similar, but higher, selectivity is observed for the conformationally locked 3-tert-butyl analogue. In contrast, both 4-methyl and 4-tert-butylcyclopentene exhibit a strong preference, 4: 1 and 7: 1, respectively, for cis hydration. Furthermore, the 3-alkylcyclopentenes give still different results. The 3-methyl derivative undergoes hydration preferentially at the 3 position with a 6: 1 preference for the trans-alcohol. On the other hand, the 3-tert-butyl olefin shows no significant regioselectivity, but a strong, 93:7, preference for trans hydration. 3, 4-Dimethylcyclopentene results in a 9: 1 predominance of the 3 isomer with only a slight preference for the cis-cyclopentanol. The presence of a methyl group in the 1 position of this system results in the formation of only the two tertiary alcohols, however, with a 3: 1 favoring of the trans-alcohol. Virtually identical regio-and stereochemical results are observed for 2, 3-di-methylcyclopentene. © 1979, American Chemical Society. All rights reserved.