Allylically Stannylated Cholestenes: The Synthesis of 3α-(Triphenylstannyl)cholest-4-ene, 7α-(Tributylstannyl)- and 7α-(Triphenylstannyl)cholest-5-en-3-one, and 7α-(Triphenylstannyl)-cholest-5-en-3β-ol - Dang, Hai-Shan; Davies, Alwyn G (Synthesis, 1992)