Cyclopentenol → (+)-ethyl (1 R)-2-pentyl-2-cyclopentene-1-acetate

Participants

Reaction Steps

A mixture of the cyclopentenol obtained according to Example 1 (5 g, 32.5 mmol) with triethyl orthoacetate (47.2 ml=42.1 g, 260 mmole, 8 eq.) was heated to 145° (temp. of oil bath 160°) under a nitrogen current in a reactor which was equipped with a Vigreux column and a condenser, while adding continuously, over 4 h, pivalic acid (232 mg, 2.28 mmole, 7 mol %) in triethyl orthoacetate (5.9 ml=5.26 g, 32.5 mmole, 1 eq.). During the reaction, the formed ethanol, as well as the ethyl acetate and a little orthoacetate, were removed by distillation. The reaction mixture was heated for 1 more hour, then cooled to 20°, hydrolyzed with diluted aqueous NaHCO3 and extracted with ether. The organic layer was washed 2x with water and once with brine, dried over Na2SO4 and evaporated, to give 15.4 g of crude product. After distillation of the heads (6.6 g, 50°/1.1×102 Pa), 5.30 g (95°/1.1×102 Pa) of (+)-ethyl (1 R)-2-pentyl-2-cyclopentene-1-acetate were obtained (yield 73%), having an enantiomeric purity of 90% e.e. (chiral column of the type Megadex® 5).

Provenance & Evidence