Oxymetallation. Part VII. Peroxymercuration of terminal, medial, and cyclic alkenes without accompanying acyloxymercuration
Ethylene, propene, styrene, cis- and trans-but-2-ene, trans-hex-3-ene, cis- and trans-stilbene, trans-prop-1-enylbenzene, cyclohexene, norbornene, and 2-methylpropene each react with mercury(II) trifluoroacetate and t-butyl hydroperoxide in dichloromethane to provide the peroxymercurials R1R3C(OOBut)·CH(HgO2C·CF3)R2. Unlike the corresponding reactions with mercury(II) acetate, competitive acyloxymercuration does not occur. The products are obtained in high yield (ca. 85%) and require little or no purification; they have been characterized by elemental analysis and 1H n.m.r. spectroscopy.
A mixture of positional isomers is obtained from prop-1-enylbenzene but the compound PhCH(OOBut)·CH(HgO2C·CF3)Me (84%) predominates. Diastereoisomeric products are obtained from the cis/trans-pairs and the spectra of the crude materials show that the reactions are stereospecific. When treated with mercury(II) trifluoroacetate and t-butyl hydroperoxide or methanol, the peroxy- and methoxy-mercurials from both cis- and trans-stilbene undergo oxidative demercuration with rearrangement to give the compounds Ph2CH·CH(OR)2, where R = OBut or Me.