[OH:1][CH2:2][C:3]1[CH:12]=[CH:11][C:6]([C:7]([O:9]C)=[O:8])=[CH:5][CH:4]=1.[OH-].[Na+]>O>[OH:1][CH2:2][C:3]1[CH:4]=[CH:5][C:6]([C:7]([OH:9])=[O:8])=[CH:11][CH:12]=1A mixture of Me pHMB (50.0 g., 0.30 mole) and 200 ml. of water containing sodium hydroxide (13.3 g., 0.33 mole) was refluxed for 3 hours. The colorless solution was filtered from a small amount (0.5 g.) of a gummy solid and extracted with methylene chloride (2 × 50 ml.). The aqueous portion was acidified with concentrated hydrochloric acid to give 37.0 g. of pHMBA: m.p. 180°-181° C. The filtrates were concentrated to 100 ml. at 100° C., cooled to 20° C., and filtered to give 6.7 g. of pHMBA (m.p. 181° C.). The combined yield of pHMBA was 43.7 g. (96%): silylation gc, 99.7% pHMBA.
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