Final answer:
NaBH4 is the preferred reagent for converting a ketone to an alcohol without affecting an ester due to its selectivity and milder reaction conditions compared to other potential reagents like LiAlH4.
Step-by-step explanation:
The best reagent to use if you want to convert a ketone to an alcohol in the presence of an ester is NaBH4. Sodium borohydride is selective enough to reduce aldehydes and ketones without affecting esters. Unlike LiAlH4, which is more reactive and can reduce esters to alcohols, NaBH4 provides a more controlled reaction, only targeting the ketone functional group.
Reagents like RMgX or R-Li are strong bases and nucleophiles, which are not suitable for this transformation in the presence of esters because they can react with the ester group as well. Raney Nickel can be used for catalytic hydrogenation but is not ideal for selective reduction in the presence of an ester since it may also affect the ester group.