Hydrochlorination stereochemistry

A similar mechanism was recently suggested for the hydrochlorination of styrene and t-butylethylene by Fahey and McPherson (1969). The proposed mechanistic scheme appears reasonable in a weakly dissociating solvent, such as acetic acid, although it seems somewhat surprising that the product distribution and the stereochemistry are insensitive to addition of diluents such as formic acid up to 1 1m. 

The 5a-configuration of the 5-chlorocholestane which results from hydrochlorination of cholest-5-ene has been confirmed by X-ray analysis. The residue from hydrochlorination of cholest-5-ene appeared to contain another compound which could not be isolated or identified as the unknown 5/8-isomer. Perhaps the possibility of its being a backbone-rearranged isomer (p. 273) should be investigated. The stereochemistry of electrophilic attack upon a A -steroid may depend critically upon subtle conformational features. Cholest-5-en-3-one, for example, reacts with bromine chloride to give products of both a- and /8-attack, whereas cholesterol is attacked almost wholly from the a-face. Discussion centres on... 

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