Normal radical relay chlorination of cholestan-3α-ol directed by an attached m-iodobenzoate ester group
affords a 9α-chloro steroid, but when the same reaction is conducted in the presence of an excess of
CBr4 the product is a 9α-bromo steroid. Similarly, when the same radical relay reaction is carried out
in the presence of an excess of (SCN)_2 rather than CBr_4, the product is a 9α-thiocyano steroid. Several
other examples of these reactions have been developed. These tandem remote functionalization reactions
succeed because an intramolecular hydrogen abstraction by a complexed-chlorine atom generates a
specific substrate radical in each case
