Addition of NaBH4 to ketones to give secondary alcohols
Description: Addition of sodium borohydride (NaBH4) to ketones gives secondary alcohols (after addition of acid)
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how come on the 4th example the alkene isn’t turned into an ether as it reacts with methanol
Alkenes need strong acid to react with alcohols to give ethers. That isn’t present here.
Is it true that NaH cannot reduce ketones and aldehydes? If so, I wonder what is the reason.
The hydride in NaH behaves like a strong base rather than a nucleophile. Since hydride is so small, it’s not polarizable and therefore not nucleophilic. BH4- is nucleophilic.
Does nabh4 also give conjugated nucleophillic addition reaction with alpha beta unsaturated ketone?
It can; you might find this to be somewhat textbook dependent. In practice, it can go either way. To get addition to occur exclusively on the carbonyl carbon, sometimes cerium trichloride is used. Google “Luche reduction”
helpful!