Reaktionsschritte
Acetic anhydride (91 μl) is added to a mixture of (±) (1S,9aS/1R,9aR) N-[(9,9a-dihydro-3-oxo-1H,3H-oxazolo[3,4-a]indol-1-yl)methyl]acetamide (X diastereomer B, EXAMPLE 11, 74 mg) in methane sulfonic acid (1 ml) at 0° over 1 minute. The mixture is stirred for 20.5 hours and allowed to warm to 20°-25° during this time. At the end of this time, a small amount of ice is added and the mixture is diluted with methylene chloride. To this mixture of sodium bicarbonate (2.4 g) is added slowly. The solvent layers are separated and the aqueous layer is extracted with additional methylene chloride (7×1 ml). The combined organic layers are dried over magnesium sulfate and concentrated to provide an oil. This oil is purified on a silica preparative plate (1000μ) by developing it in methanol/methylene chloride (5/95, 3×) which provides the title compound, NMR (CDCl3, 300 MHz) 7.88, 7.84, 7.43, 6.40, 4.62, 4.57, 3.75, 3.36, 3.13, 2.58 and 2.08 δ; CMR (CDCl3, 75.47 MHz) 23.15, 26.62, 34.24, 41.02, 61.84, 83.26, 114.37, 125.53, 129.86, 132.98, 134.2, 144.1, 154.7, 170.6 and 196.5 δ; IR (CHCl3) 3660, 3440, 2980, 2920, 1760, 1670, 1600, 1480, 1420, 1350, 1260, 1120, 1050, 980 and 700 cm-1 ; MS (m/e) 288, 244, 229, 216, 201, 185, 170, 160, 144, 130, 118, 85, 73 and 43, exact mass calcd for C15H16 --N2O4 (288.1110), found 288.1105.
