Reaction #2649

Reaction equation

triethylamine

vinyl acetate

chloroform

Cis-4-tert-butyloxy-cyclopent-2-enol

→

(-)-acetic acid cis-4-tert-butyloxy-cyclopent-2-enyl ester

Yield 50.0%

Solvents

tert-butyl methyl ether

Conditions

Workup

1. 1
   FiltrationThe reaction is then filtered through diatomaceous earth
2. 2
   Concentrationthe filtrate is concentrated under vacuum
3. 3
   OtherThe products are separated by chromatography on silica gel (10% to 20% ethyl acetate/hexane)

Procedure

Cis-4-tert-butyloxy-cyclopent-2-enol (485 mg, 3.1 mmol, prepared in example 9) is dissolved in tert-butyl methyl ether (8.6 mL, anhydrous). To the solution is added triethylamine (0.7 eq), pancreatin (3 wt eq, available from Sigma Chemical Company), and vinyl acetate (5 eq). The reaction is allowed to stir for 17 hours at room temperature. The reaction is then filtered through diatomaceous earth and the filtrate is concentrated under vacuum. The products are separated by chromatography on silica gel (10% to 20% ethyl acetate/hexane) to provide (-)-acetic acid cis-4-tert-butyloxy-cyclopent-2-enyl ester (B, 50% yield, 76% ee), [α]D =-10.9°, (c=0.98, chloroform), 1H NMR (CDCl3) δ5.94 (d, 1H, J=5.5 Hz), 5.89 (d, 1H, J=5.5 Hz), 5.46 (appt, 1H, J=5.5 Hz), 4.52 (appt, 1H, J=5.5 Hz), 2.8 (m, 1H), 2.0 (s, 3H), 1.6 (d appt, 1H, J=4.8, 14 Hz), 1.22 (s, 9H); 13C NMR (CDCl3) δ171.2, 138.6, 131.6, 77.4, 77.2, 41, 28.7, 28.6, 21.4; IR (neat) νmax 2976, 1738, 1364, 1242, 1196, 1067, 1020 cm-1 ; CIMS m/e (% relative intensity) 199 (M+H+, 4), 139 (M+H+ -AcOH, 70), 83 (100), and (-)-cis-4-tert-butyloxy-cyclopent-2-enol (A, 194 mg, 40% yield, >98% ee), [α]D 17.2°, (c=1.09, chloroform) as a yellow oil.

Source