Carbonyls to alcohols reactions

Organolithium and Grignard reagents

aldehydes and ketones to alcohols

Mechanism that organolithium and grignard reagents undergo with carbonyls?

Addition

Preparation of organolithium/grignard reagents?

Treat the corresponding alkyl halide with the metal, in THF or diethyl ether solvent.

Why is THF or diethyl ether used?

Polar aprotic solvent needed, THF H-bonds to metal to aid stability and stop it decomposing.

NaBH4

nucleophilic, reduces aldehydes and ketones to alcohols

Solvent used with NABH4

EtOH or iPrOH, as they react slowly with NaBH4 to form reducing agent in situ

LiAlH4

nucleophilic, reduces even weakly electrophilic carbonyl groups to alcohols (aldehydes, ketones, esters, amides (to amines), carboxylic acids)

Solvents for LiAlH4

Reacts with protic solvents, so THF or Et2O

DIBAL-H

electrophilic, reduces aldehydes, ketones, esters and tertiary amides.

How does DIBAL-H work?

Central Al has empty p orbital which accepts lp from C=O oxygen, making C more positive, so H from DIBAL-H moves to carbonyl as pi-bond breaks. Aq work up replaces O-Al bond with O-H.

For esters, 1 equ. DIBAL at -78 degrees forms

aldehyde

For esters, 2 equ. DIBAL at 0 degrees or r.t. forms

alcohol

For hydration, water is a poor nucleophile so we must

increase electrophilicity of carbonyl or increase nucleophilicity of water

Hydration in acidic conditions

C=O-H makes C more electrophilic for the water to react

Hydration in basic conditions

OH is better nucleophile than water

More substituted carbonyls are

more stable due to inductive effects of side groups

More substituted diol products are

less stable because from sp2 to sp3 steric clash between substituents increases