Rationale for the Selectivity of the Conversion from 14 to 15
Due to the great bulkiness of molecule 14 after the oxygen of the carbonyl bonds to Stryker’s catalyst, [(Ph3P)CuH]6 , PhSiH3 could only approach molecule 14 from the less hindered side to donate a hydride to the carbocation. If the other double bond had pushed its electrons onto the carbon with the carbonyl group, a carbocation would form at the carbon circled in red below. Because of the bulkiness of PhSiH3, it would not be able to approach the molecule and donate a hydrogen to that carbon.
