Phosphorus oxychloride → (1R,5S)-(+)-4,4,6,6-Tetramethyl-3-oxabicyclo[3.1.1]heptan-2-one

Participants

Reaction Steps

To a solution of 2.66 g (14.28 mmol) of alcohol 3a in 15 mL of pyridine was added dropwise in 1.40 mL (15.00 mmol) of phosphorus oxychloride at ice-water cooling. The mixture was stirred at room temperature for 24 h, poured onto 75 g of ice, and extracted with ether. The ether extracts were washed with water, 2N hydrochloric acid, then water, saturated aqueous solution of sodium hydrogen carbonate, and brine. After drying over sodium sulfate, the solvent was removed, and the residue was purified by chromatography (30/70, ethyl acetate/hexanes) to afford 1.8 g (10.71 mmol) of pure lactone 4a in 75% yield. Optical purity: 80% ee; [α]24D+5.0 (c 0.1, MeOH); 1H NMR (CDCl3): δ 1.14 (3H, s), 1.37 (3H, s), 1.38 (3H, s), 1.49 (3H, s), 1.81 (1H, d, J=10.59 Hz), 2.10 (1H, dd, J=6.05, 5.67 Hz), 2.48 (1H, ddd, J=10.59, 5.67, 5.30 Hz), 2.63 (1H, dd, J=6.05, 5.30 Hz); 13C NMR (CDCl3): δ 175.04, 82.44, 50.34, 50.01, 40.91, 29.11, 26.11, 25.81, 25.27, 25.25; EI-MS m/z (%): 153 (26), 125 (20), 110 (40), 109 (55), 95 (100), 83 (27), 69 (72), 68 (78), 67 (60), 55 (42), 43 (35), 41 (38); HREIMS: obsd. 153.0911, calcd. for C9H13O2 (M+—CH3): 153.0916.

Provenance & Evidence