Acetaldehyde → (E)-(2S)-6-phenylhex-5-en-3-yn-2-ol

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A flask containing Zn(OTf)2 (Zinc triflate purchased from Fluka was found to give the best results, other vendor's proved inefficient; 557 mg, 1.50 mmol) and (−)—N-methylephedrine (275 mg, 1.50 mmol) was added toluene (1.5 mL) and Et3N (209 μL, 1.50 mmol) at 23° C. under a nitrogen atmosphere. The resulting mixture was stirred for 2 h at 23° C. before but-1-en-3-ynyl-benzene (192 μL, 1.50 mmol) was added in one portion. After stirring for 15 min at 23° C., the reaction was cooled to 0° C., then acetaldehyde (168 μL, 30.0 mmol) was added at the same temperature in one portion. The resulting mixture was warmed to 23° C. and stirred for 35 h, then quenched by the addition of saturated aqueous NH4Cl (3 mL). The mixture was poured into a separatory funnel and diluted with EtOAc (5 mL). The layers were separated and the aqueous layer was extracted with EtOAc (3×3 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated in vacuo. Purification of the residue via flash chromatography (0→20% EtOAc/hexanes) afforded compound 7 (106 mg, 41%, 72% ee; the ee was determined after making the acetate ester) as a pale yellow oil.

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