[3685-19-0] · C5H6O · (Z)-1-Methoxy-1-buten-3-yne · (MW 82.11)
(convenient building block for synthesis of spiroacetals, dialkynes, enones, and dienes)
Physical Data: bp 52 °C/28 mmHg.
Solubility: slightly sol H2O; sol standard organic solvents.
Form Supplied in: 50 wt % solution in methanol-water.
Purification: can be obtained anhydrous by saturation of the solution of 1-methoxy-1-buten-3-yne in methanol-water with solid NaCl followed by extraction with ether and distillation under reduced pressure (52 °C/28 mmHg).
Handling, Storage, and Precautions: store under nitrogen.
(Z)-1-Methoxy-1-buten-3-yne is readily deprotonated by n-Butyllithium in THF. The resulting anion reacts with alkyl halides, carbonyl compounds, and trialkylchlorosilanes. The anion of 1-methoxy-1-buten-3-yne has been used in a direct synthesis of spiroacetals (eq 1).2 When (Z)-1-methoxy-1-buten-3-yne is treated with 2 equiv of n-butyllithium, the monoanion of 1,3-butadiyne is formed (eq 2).3 If 3 equiv of n-butyllithium are used, the dianion of 1,3-butadiyne is generated. (Z)-1-Methoxy-1-buten-3-yne also serves as a convenient precursor to a,b;g,d-unsaturated aldehydes by a sequence involving addition of its anion to an aldehyde followed by reduction of the resulting acetylenic alcohol using Lithium Aluminum Hydride and acid-mediated hydrolysis (eq 3).4
1-Methoxy-1-buten-3-yne can be alkylated and treated with dialkylboranes to form vinylboranes (eq 4).5 The regiochemistry of the hydroboration reaction appears to be directed by the methoxy group. The vinylborane can be oxidized to provide a b-methoxy enone. The hydrozirconation of 1-methoxy-1-buten-3-yne proceeds regioselectively to form a diene which reacts with N-(phenylselenyl)phthalimide to afford 1-phenylselenyl-4-methoxy-1,3-butadiene in good yield.6 1-Methoxy-1-buten-3-yne also reacts with cyclopropyl carbene chromium complexes to form cyclopentenones.7 (Z)-1-Methoxy-1-buten-3-yne can also be converted into a copper salt which reacts with aryl iodides, acid chlorides, and alkyl halides.8
George A. Kraus
Iowa State University, Ames, IA, USA