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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3hc075

Which of the following methods convert (E)-but-2-ene into meso-butane-2,3-diol? Select all that apply.

ACold, dilute, alkaline $KMnO X_{4}$
B(i) $CH X_{3} CO X_{3} H$ (peracid) to give the epoxide; (ii) $H X_{3} O X^{+}$
C(i) performic acid, $HCO X_{3} H$ ; (ii) $H X_{3} O X^{+}$
D(i) $OsO X_{4}$ ; (ii) $NaHSO X_{3} / H X_{2} O$

Answer: B, C

Permanganate and osmium tetroxide add both OH groups to the same face (syn), and syn addition to the E-alkene gives the racemic (2R,3R)/(2S,3S) diol. Epoxidation is stereospecific, giving the trans-epoxide, and acid-catalysed opening is anti. Anti hydroxylation of the E-alkene gives the meso diol, so both peracid-then-acid routes qualify.

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