Oxymetallation. Part IX. Bromodemercuration of peroxymercurials derived from terminal, medial, and cyclic alkenes to give β-bromoperoxides

Abstract

Each of the peroxymercurials R¹R³C(OOBu^t)·CH(HgBr)R² derived from ethylene, propene, 2-methylpropene, but-2-ene, hex-3-ene, stilbene, prop-1-enylbenzene, cyclohexene, and norborn-2-ene reacts with bromine in dichloromethane to afford the corresponding β-bromo-peroxide R¹R³C(OOBu^t)·CHBrR², in ca. 85% yield; the new compounds have been characterised by ¹H n.m.r. spectroscopy. The bromo-peroxides derived from non-terminal alkenes are obtained as 1 : 1 mixtures of diastereoisomers except for the norbornene derivative where the ratio of isomers is 65 : 35. The extent of racemisation is considerably reduced by carrying out the bromodemercuration in pyridine; isomer ratios of 4 : 1 are thus readily obtained.