LiAlH4 vs NaBH4

[NSMedical]

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Hi guys!

Here is a direct link to an image regarding the synthesis I have a question on!
http://tinypic.com/r/209kch3/8

I understand LiAlH4 is stronger than NaBH4 and that NaBH4 does not react with esters. However, wouldn't the LiAlH4 reduce both carbonyls? What reagent would I use to retain the ketone and reduce the ester to a primary alcohol?

Also, is there a difference between using LiAlH4/CH3OH/H3O+ VS LiAlH4/diethyl ether/H3O+?

Any help would be appreciated. Thank you!

 

[Czarcasm]

Hi guys!

Here is a direct link to an image regarding the synthesis I have a question on!
http://tinypic.com/r/209kch3/8

I understand LiAlH4 is stronger than NaBH4 and that NaBH4 does not react with esters. However, wouldn't the LiAlH4 reduce both carbonyls? What reagent would I use to retain the ketone and reduce the ester to a primary alcohol?

Also, is there a difference between using LiAlH4/CH3OH/H3O+ VS LiAlH4/diethyl ether/H3O+?

Any help would be appreciated. Thank you!

I could be wrong here since I haven't reviewed orgo in months, but this was my approach: 1. LiAlH44 2. H3O+ 3. TsCl 4. PCC 5. H2O (in absence of acid). I believe this is one of those instances where a protecting group is required though.

LiAlH4 (not NaBH4) is strong enough to reduce esters, aldehydes, and ketones.
H30+ workup step protonates the negatively charged oxygen's (O- to -OH groups).
TsCl is really bulky and makes primary alcohol's a good leaving group (changes primary -OH to OTs)
PCC oxidizes any primary or secondary alcohols (changes secondary -OH to Ketone)
H2O attacks OTs and changes it into an -OH (but in the absence of acid, it's not a good enough nucleophile to attack the carbonyl).

 

[premed1001]

I think ketones are protected by turning them into ketals.

So if you turn the ketone end into a ketal it won't react when you add LiAlH4 or NaBH4 to react the other end.

I think at this point either NaBH4 or LiAlH4 can reduce the ester all the way to a alcohol.

I do not know how to unprotect the ketal back to a ketone.

 

[DrknoSDN]

http://en.wikipedia.org/wiki/Protecting_group

Same reaction as OP. w/ mechanism. Ketal/Acetyl blocking groups also avoid steric factors around the carbonyl like this cyclic molecule.

 

[premed1001]

http://en.wikipedia.org/wiki/Protecting_group

Same reaction as OP. w/ mechanism. Ketal/Acetyl blocking groups also avoid steric factors around the carbonyl like this cyclic molecule.

Thanks!