Prostaglandins borane reduction

In the early work on the synthesis of prostaglandins, zinc borohydride was used for the reduction of the 15-ketone function and a 1 1 mixture of epimeric 15(S)- and 15(/ )-alcohols was generally obtained. Subsequent studies led to reaction conditions for highly selective reduction to the desired 15(S)-alcohol. Some of the results are summarized in the following table. The most practical method is E which utilizes borane as the stoichiometric reductant and a chiral, enzyme-like catalyst which is shown. 

The hydrosilylation of ketones is referred to above when a chiral phosphine-platinum (ii) complex is used as catalyst, chiral alcohols are obtained, as their silyl ethers, in optical yields of 5-18%. Chiral alcohols are also obtained in 15-20 % optical yield by condensation of ketones with magnesium alcoholates derived from N-methylephedrine. A study of the chiral reducing system, a-phenylethylamine-borane, has been referred to previously, as has Corey s refinement of prostaglandin reduction. 

---