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At room temperature, compound 31a (71.88 g, 1 eq.) and p-toluene sulfonic acid (74.4 g, 1.2 eq.) were dissolved in MeOH (640 mL). The reaction mixture was refluxed for 7 days. The solvent was then removed under vacuum, and the residue was recrystallized in acetone. The product was isolated by filtration and dried over P2O5 to give compound 32a as a white powder in 76% yield. 1H NMR (CDCl3, 400 MHz): δ (ppm) 1.38 (q, J=7.76 Hz, 2H), 1.71 (q, J=7.76 Hz, 2H), 1.99 (q, J=6.98 Hz, 2H), 2.38 (s, 3H), 2.70 (t, J=5.17 Hz, 3H), 2.87-2.93 (m, 2H), 4.92-4.99 (m, 2H), 5.67-5.73 (m, 1H), 7.20 (d, J=7.76 Hz, 2H), 7.75 (d, J=7.76 Hz, 2H), 8.62 (br s, 2H).

1. temperatureThe reaction mixture was refluxed for 7 days
2. customThe solvent was then removed under vacuum
3. customthe residue was recrystallized in acetone
4. customThe product was isolated by filtration
5. dry with materialdried over P2O5