Chemistry of oxaziridines. 13. Synthesis, reactions, and properties of 3-substituted 1,2-benzisothiazole 1,1-dioxide oxides

Abstract

Cupric oxide (0.007 g, 0.08 mmol) and anhydrous potassium carbonate (0.094 g, 0.68 mmol) were added. The tube was flushed with argon, and diiodomethane (82 p L , 1.02 mmol) was added. The tube was sealed and heated to 80-90 "C (oil bath temperature) for 24 h. After the mixture had been cooled to room temperature, aqueous HCl(4 mL of 1 N HCl in 20 mL of HzO) was added and the solution extracted with ethyl acetate (5 X 20 mL). The combined extracts were washed with water (1 X 50 mL), dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure, to give a brown solid. Radial chromatography with 10% ethyl acetate/hexanes as eluent yielded (f)-pterocarpin (3) (35 mg, 35%), anhydropisatin (15,1.5 mg, 2%), and a mixture of 3 and 15 (14.6 mg, 11% and 4%, respectively, by 'H NMR). Flash column chromatography using silver nitrate impregnated silica gel (prepared by swirling SiOz in 4% AgN03/CH3CN and then evaporating the solvent under reduced pressure) gave pure (f)-pteroaarpin (3) and anhydropisatin (15). Recrystallization of 3 from ethyl acetate/hexanes gave cylindrical colorless crystals: mp 190-192 "C (lit. mp 168-169 "CZc and 185-186 oC24b). Physical data for 3: R (30% EtOAc/hexanes) 0.52; Rf [lo% EhO/hexanes on AgN& impregnated silica gel plate (made by dipping in 4% AgN03/CH3CN solution)] 0.14; 'H NMREbJ (300 MHz) 3.44-3.53 (m, 1 H), 3.66 (t, 1 H, J = 10, 3.79 (8, 3 H), 4.23 (dd, 1 H, J = 11,4.4), 5.49 (d, 1 H, J = 6.7), 5.90 (2 overlapping d, 2 H), 6.43 (s, 1 H), 6.47 (d, 1 H, J = 2.6), 6.64 (dd, 1 H, J = 8.0, 2.5), 6.72 (s, 1 H), 7.40 (d, 1 H, J = 8.0). Physical data for 15:14 Rf [lo% EhO/hexanes on AgN03 impregnated silica gel plate (made by dipping in 4% AgN03/CH3CN solution and then drying] 0.18; 'H NMR (300 MHz) 3.80 (8, 3 H), 5.52 (s, 2 H), 5.99 (s, 2 H), 6.53 (d, J = 2.2, 1 H), 6.56 (dd, J = 2.2, 8, 1 H), 6.73 (8, 1 H), 7.02 (s, 1 H), 7.37 (d, J = 8, 1 H); EIMS m/z (relative intensity) 296 (loo), 147 (12), 139 (13), 69 (12).Acknowledgment. We thank Michael Kaufman for technical assistance.The synthesis, properties, and reactions of 3-substituted 1,2-benzisothiazole 1,l-dioxide oxides 8, highly stable examples of 3,3-disubstituted N-sulfonyloxaziridinea 3, are described. These new N-sulfonyloxaziridinea are prepared in high yield by oxidation of the corresponding sulfonimines 7. The bicyclic sulfonimines were prepared by treatment of saccharin (5) or preferably pseudosaccharin ethyl ether 6 with organolithium reagents. Kinetic studies of the oxidation of sulfoxides to sulfones and the epoxidation of limonene reveal that these new oxidizing reagents exhibit reduced reactivity, but greater selectivity, compared to oxaziridines of type 1, in their oxygen-transfer reactions due to greater steric hindrance of the active-site oxygen. This is reflected in lower rates of oxidation and in improved cis/trans selectivity for the epoxidation of (+)-limonene. (5) Davis, F. A,; Haque, M. S.; Ulatowski, T. G.; Towson, J. C. J. Org. Chem. 1986,51,2402. (b) Davis, F. A.; Haque, M. S. J. Org. Chem. 19...

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