C1([C:6](O)=[O:7])CCCC=1.COC1C=CC(CS)=CC=1.CO[C:21]1[CH:26]=[CH:25][C:24]([CH2:27][S:28][CH:29]2[CH2:33][CH2:32][CH2:31][CH:30]2[C:34]([OH:36])=[O:35])=[CH:23][CH:22]=1.C1CCCCC1>N1CCCCC1.C(O)(=O)C>[CH3:6][O:7][C:23]1[CH:22]=[CH:21][CH:26]=[CH:25][C:24]=1[CH2:27][S:28][CH:29]1[CH2:33][CH2:32][CH2:31][CH:30]1[C:34]([OH:36])=[O:35]
A solution of 1-cyclopentene carboxylic acid (1.68 g., 15 mmole) and p-methoxy-α-toluenethiol (2.17 ml., 15.6 mmole) in piperidine (3.9 ml.) is flushed with argon and heated under reflux, protected by a drying tube, for 12 hours. The mixture is then partitioned between ethyl ether (100 ml.) and 1N hydrochloric acid (3×40 ml.). The organic phase is stirred with activated charcoal (about 0.5 g.), dried (MgSO4), filtered through Celite, and concentrated in vacuo to an orange-yellow oil. This oil is recrystallized successively (3 times) from cyclohexane/hexane to yield 1.75 g. of 2-[[(4-methoxyphenyl)methyl]thio]cyclopentanecarboxylic acid as a tan, granular solid; m.p. 63°-66°. TLC (silica gel, cyclohexane:acetic acid, 8:1) Rf =0.23.
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