Question

Lithium borohydride (LiBH4) is a useful reducing agent, as it is more selective than LAH but less selective than NaBH4. Unlike the latter, LiBH4 will reduce esters. However, it will not reduce amides. This selectivity is frequently employed by synthetic organic chemists. For example, during a synthesis of (—)-croalbinecine, a natural product with cytotoxic properties, compound 1 was converted to compound 3, as shown below (J. Org. Chem. 2000, 65, 9249–9251).

Answer 1

Reducing agents

Among the given reducing agents, weakest reducing agent is NaBH4, thus more chemoselective and reduces specifically only the aldehyde and ketones to corresponding alcohols.

LiBH4 is the second most reactive agent, which reduces esters but not amides.

Whereas, lithium aluminium hydride is a strong reducing agent and it reduces almost all of the functional groups (not the olefins and alkynes). It is least chemoselective but extremely useful in common organic synthesis where selectivity is not a concern.