2-Methyl-2-pentenal → 4-Methylhept-4-en-1-yn-3-ol

To a solution of ethynyl magnesium bromide (prepared from 2.91 g of magnesium) in 100 ml of tetrahydrofuran, was added dropwise 9.8 g of 2-methyl-2-pentenal at a temperature from 0° C to 10° C under cooling with ice-bath. The resulting reaction solution was stirred for 3 hours at room temperature to complete the reaction and then the reaction solution was poured into a saturated ammonium cloride solution with 50 g of ice. After stirring, the solution was extracted twice with 100 ml of ether and the organic layers were combined, and then washed with 50 ml of a saturated sodium chloride solution. After the organic layer had been dried over anhydrous sodium sulfate, the ether was evaporated. The remaining liquid was purified by distillation at reduced pressure to obtain 10.2 g of a colorless oily 1-ethynyl-2-methyl-2-pentenyl alcohol, b.p. 85°-88° C/20 mmHg.