Ethyl 1-propenyl ether → 2-(2-Formylpropyl)-3-isopropenyl-1-methyl-cyclopent-1-ene

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15 drops of 85% phosphoric acid were added to a mixture, cooled to -30° C in a laboratory autoclave, of 76 g of 3-isopropenyl-1-methyl-2-methylene-cyclopentan-1-ol and 130 g of ethyl 1-propenyl ether. After gassing with nitrogen, the autoclave was brought, in an oil bath of 180° C, to an internal temperature of 150° C (this took about 15 minutes) and held at this temperature until a distinct drop in pressure occurred (about 75 minutes). The reaction mixture was then quenched, taken up in ether, washed with aqueous bicarbonate solution and water, the solution dried over anhydrous magnesium sulphate and concentrated under reduced pressure. The crude product (135 g), obtained as a yellow oil, was fractionated and yielded 64 g (67%) of pure 2-(2-formylpropyl)-3-isopropenyl-1-methyl-cyclopent-1-ene having woody, earthy, musty fragrance; boiling point 0.005 = 51° C; nD20 = 1.4825; IRfilm : νmax = 3090, 2730, 1735, 1645, 1460, 1380 and 898 cm-1.

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