A researcher has a sample of a chiral alkyne, (S)-4-methyl-1-hexyne. Which reaction will convert this alkyne to a chiral alkene with (E) geometry?
- H₂ (1 eq.), PtO₂
- H₂ (1 eq.), Lindlar's catalyst
- Na, NH₃(l) (correct answer)
- H₂SO₄, H₂O, HgSO₄
Explanation: The goal is to reduce the alkyne to an alkene with (E) or trans geometry while preserving the existing stereocenter. The dissolving metal reduction using Na in liquid NH₃ accomplishes the stereoselective formation of an (E)-alkene via an anti-addition mechanism. The reaction conditions do not affect the stereocenter at C4. H₂/Lindlar's catalyst would give the (Z)-alkene. H₂/PtO₂ would reduce the alkyne to an alkane. Hydration (H₂SO₄, H₂O, HgSO₄) would produce a ketone.