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Henbest and Nicholls. 227 41. Aspects of Stereochemistry. Part XII.* A Speci$c Directing Effect in the Mercuration of Some 4-Substituted cycloHexenes and cis-Hex-3 -ewZ. By H. B. HENBEST and B. NICHOLLS.Functional groups can exert a directing effect on the stereochemistry of addition of HgX and OR at a double bond, in at least two ways. In the first, the reactions are completed by a suitably placed acid or alcohol group acting as an intramolecular nucleophile, and lactones or ethers are formed: some new examples are given in the bicydoheptene series and with tvans-hex-3-enol. A second, new directing effect has been encountered with certain 4-substituted cyclohexenes and cis-hex-3-enol : here hydroxyl or other Lewis base groups (OMe, OAc, CO,Me, CH,*OH, CN) promote stereospecific addition of acetoxymercuri-groups and of anions (from solvent) to the double bond. A possible mechanism for these additions is discussed. As the mercuri-groups in these adducts can be removed by reduction, a two-step method for the specific addition of water or methanol to certain double bonds becomes available.

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