Selective Reduction to 1° Alcohols

$$\text{R-COOH} \xrightarrow{\text{1. LiAlH}_4 \, / \, \text{Ether} \quad \text{or} \quad \text{B}_2\text{H}_6 \, / \, \text{THF}} \text{Alkoxide Intermediate} \xrightarrow{\text{2. H}_3\text{O}^+} {R-CH}_2\text{OH}$$

Concept: Complete reduction of the carbonyl and hydroxyl components down to a primary alcohol terminal group. This requires highly aggressive hydride donors or specialized borane systems.

Notation:

• $$\text{LiAlH}_4$$ /$$\text{B}_2\text{H}_6$$ = Capable reducing agents ($$\text{B}_2\text{H}_6$$is highly chemoselective and does not attack esters or nitro groups);
• $$\text{NaBH}_4$$ = Sodium borohydride cannot reduce carboxylic acids due to their low electrophilicity.