The compound shown is treated with NaBH4 in ethanol at 0 degC (1 equivalent hydride-donor in the cold), then dilute acid. Which structure is the major product?

JEE Main levelSingle correct optionDifficulty 2 of 3ro224

The compound shown is treated with $NaBH X_{4}$ in ethanol at $0^{\circ} C$ (1 equivalent hydride-donor in the cold), then dilute acid. Which structure is the major product?

The compound is methyl 4-formylbenzoate.

NaBH X_{4}

is mild: it reduces the aldehyde quickly and leaves the ester untouched, giving methyl 4-(hydroxymethyl)benzoate. The diol would need

LiAlH X_{4}

, and the structure with the ester reduced but the aldehyde kept is the wrong chemoselectivity.