The kinetics and mechanisms of additions to olefinic substances. Part 13. Reactions of 3-substituted cholest-5-enes with sources of electrophilic bromine
Abstract
The kinetics of second-order bromination in acetic acid, and of third-order bromination in chlorobenzene, have been examined for a series of 3β-substituted cholest-5-enes; the results confirm that the rates of these reactions are subject to polar influences approximately of the magnitude expected for a substituent insulated by two saturated carbon atoms from the site of development of the carbocationic centre. The products of reactions of a number of these substrates with sources of electrophilic bromine and chlorine, in chlorobenzene, chloroform, and acetic acid as solvents, have been investigated by 1H n.m.r. spectroscopy. In most cases the main products are the expected 5α-halogeno-6β-substituted adducts. 5β,6α-Adducts are formed in minor amounts also in the bromination of 3β-trifluoroacetoxycholest-5-ene, and in the reactions of a number of 3β-substituted cholest-5-enes with bromine chloride in deuteriochloroform and in chlorobenzene. Some of the mechanistic implications of these findings are discussed.