8a-Formyloxy-14,15-dinorlabdan-13-one [(-)-4-((1R,2R,4aS,8aS)-2-Formyloxy-2,5,5,8a-tetramethyldecahydro-1-naphthalenyl)-2-butanone]

To a stirred solution of a mixture of E/Z isomers 1 (81 mg, 0.22 mmol, 45:55 ratio) in acetone (5 mL) was added a mixture of KMnO4 (122 mg, 0.77 mmol) and anhydrous MgSO₄ (120 mg) at 10 °C [1]. After stirring for 10 min reaction was allowed to warm to room temperature. Then another portion of KMnO4 (25 mg, 0.16 mmol) and anhydrous MgSO₄ (25 mg) was added. After 20 min the crude was filtered over Celite and the clean solution evaporated under reduced pressure to yield a residue which was solved in Et₂O (25 mL). This solution was washed with brine (3×10 mL), dried over anhydrous Na₂SO₄ and the solvent evaporated under reduced pressure to yield a residue (61 mg) which was purified by flash chromatography on silica gel, using a 2:3 hexane/Et₂O mixture as eluent, to give the title compound 2 (50 mg, 0.16 mmol, 73%).

Mp: 66.0-67.4 °C (white crystals, from hexane).

[a]_D = -22.3° (c 1.01 cg·mL^-1, CHCl₃).

IR (KBr, n, cm^-1): 1722, 1198, 1165 (OOCH), 1696 (CO).

¹H NMR (300 MHz, CDCl₃, d, ppm): 0.79 (3H, s, Me_b-4), 0.86 (3H, s, Me-10), 0.88 (3H, s, Me_a-4), 1.52 (3H, s, Me-8), 2.13 (3H, s, Me-13), 0.93-1.84 (13H, m, H-1,2,3,5,6,7a,9,11), 2.43-2.69 (3H, m, Hb-7, H-12), 8.02 (1H, s, OOCH).

¹³C NMR (75 MHz, CDCl₃, d, ppm): 39.48 (C-1), 18.17 (C-2), 41.67 (C-3), 33.04 (C-4), 55.50 (C-5), 19.87 (C-6), 39.48 (C-7), 88.99 (C-8), 57.95 (C-9), 39.48 (C-10), 19.26 (C-11), 46.37 (C-12), 208.98 (C-13), 29.78 (C-16), 21.03 (C-17), 33.21 (C-18), 21.32 (C-19), 15.42 (C-20), 160.28 (OOCH).