Reaction Steps
To a stirring solution of aldehyde 23 (26 mg, 0.028 mmol, 1.0 equiv) in 2-methyl-2-butene (400 μL) and tBuOH (400 μL), in a 10 mL rb flask at rt, was added a 1.25 M aqueous solution of KH2PO4 (134 μL). The mixture was cooled to −10° C., and NaClO2 (80%, 16 mg, 0.140 mmol, 5.0 equiv) was added in one portion. The reaction mixture stirred vigorously at −10° C. for 1.5 h, and was then quenched with aqueous pH 4 buffer solution (1 mL). The phases were separated, and the aqueous phase was extracted three times with Et2O (5 mL). The combined organic phases were dried over Na2SO4, filtered, and concentrated under reduced pressure. Purification was accomplished using flash column chromatography with a 2×13 cm silica gel column, eluting with 3% MeOH/CH2Cl2, collecting 13×50 mm test tube fractions. The product containing fractions (7-10) were combined and concentrated under reduced pressure to provide pure carboxylic acid 8 (26 mg, 99%) as a clear viscous oil: Rf=0.10 (30% EtOAc/hexanes); [α]D20=+6.7 (c=0.780, CHCl3); 500 MHz 1H NMR (CDCl3) δ 7.38-7.28 (m, 5H), 7.25 (d, J=8.8 Hz, 2H), 6.88 (d, J=8.8 Hz, 2H), 6.06 (d, J=16.1 Hz, 1H), 5.47 (dd, J=16.1, 6.3 Hz, 1H), 4.80 (s, 2H), 4.73 (m, 2H), 4.67 (s, 1H), 4.65-4.62 (m, 2H), 4.61 (s, 1H), 4.57 (d, J=10.6 Hz, 1H), 4.47 (d, J=10.7 Hz, 1H), 4.14-4.05 (m, 3H), 3.86-3.75 (m, 2H), 3.80 (s, 3H), 3.56-3.41 (m, 3H), 3.30 (s, 3H), 2.66 (dd, J=15.1, 5.4 Hz, 1H), 2.58 (dd, J=15.6, 5.9 Hz, 1H), 2.47-2.43 (m, 2H), 2.28 (m, 4H), 2.05-1.90 (m, 8H), 1.83-1.76 (m, 1H), 1.75-1.65 (m, 1H), 1.59 (ddd, J=14.3, 6.4, 6.4 Hz, 1H), 1.52 (ddd, J=13.5, 9.4, 3.5 Hz, 1H), 1.16 (d, J=6.8 Hz, 3H), 1.14 (s, 3H), 0.91 (s, 3H), 0.88 (s, 9H), 0.08 (s, 6H); 125 MHz 13C NMR (CDCl3) δ 159.6, 144.4, 144.3, 137.9, 135.5, 130.2, 129.7, 129.1, 128.6, 128.1, 127.9, 114.1, 109.1, 104.0, 93.2, 79.5, 75.2, 75.1, 75.0, 72.9, 70.7, 69.7, 69.5, 55.5, 52.8, 44.3, 42.9, 41.9, 41.2, 40.9, 40.6, 40.0, 38.2, 37.6, 30.7, 26.1, 22.9, 22.3, 18.3, 14.0, −3.9, −4.4; HRMS (EI+) calcd for C53H76O11Si (M-MeOH) 916.5162. found 916.5107.
