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Procedure: 50 mL
1-neck flask, stirbar, cap Dissolved
0.535 g of ester I in 25 mL of absolute
MeOH. Added 0.523 g of LiOH-H2O. Stirred at rt.
After 24 h, TLC (30:70 EtOAc-hexanes, PMA) showed product spot at Rf
0.11. Added 5 mL of water and
stirred for 30 min. The reaction
mixture was concentrated by rotary evaporation to about 5 mL and the pH was
lowered to 3 with 1.0 M HCl. The
mixture was extracted with EtOAc.
The organic layer was dried over MgSO4, filtered and the
solvent was removed by rotary evaporation. The product was a clear, colorless oil and was sufficiently
pure at this stage. 1H NMR (CDCl3,
300 MHz) d 4.35 (q, J = 6.6 Hz, H2, 1H), 1.45 (d, J = 6.6 Hz, H3, 3H), 0.92 (s, SiC(CH3)3,
9H), 0.13 (s, Si(CH3)2, 6H). notes The hydrolysis of esters with
hydroxide proceeds by reversible nucleophilic addition of hydroxide to the
ester carbonyl followed by reversible elimination of alkoxide to afford the
acid which is immediately deprotonated to the carboxylate. It is this last step which drives the
reaction to completion as it is the only step in the sequence which is not
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