JEE Main · 2021 · 16 Mar 2021 · Shift 1 · Chapter_pending

DIBAL-H (diisobutylaluminum hydride) at low temperature in a non-polar solvent (toluene, $-78^{\circ }\text{C}$) selectively reduces esters to aldehydes. The lactone (cyclic ester) is reduced to a hemiacetal intermediate, which upon acidic hydrolysis ($\mathrm{H}{}_3\mathrm{O}{}^{+}$) opens to give a hydroxy aldehyde. Product P is the hydroxy aldehyde shown in option (D).