In recent years 2-sulfonyl-and 2-sulfamyloxaziridines, la and lb, respectively, have received considerable attention as selective aprotic oxidizing reagents for a large variety of substrates. These reagents oxidize sulfides (selenides) to sulfoxides (selenoxides) without overoxidation.2,3 They selectively oxidize thiones to sulfines4 5and epoxidize alkenes.6 The aprotic nature of these reagents has made possible the facile syntheses of alcohols and phenols by hydroxylation of organometallic reagents,6 the oxidation of enolates to -hydroxy carbonyl compounds,7 and the synthesis of extremely acid-sensitive species such as -siloxy epoxides8 and sulfenic acids.9 Optically active 2-sulfonyl-and 2-sulfamyloxaziridines la,b afford the highest stereoselectivities reported for the oxidation of nonfunctionalized sulfides (up to 91% ee)1 and alkenes (up to 61% ee).5c The asymmetric oxidation of prochiral enolates to optically active -hydroxy carbonyl compounds (up to 95% ee) by (+)-and (-)-(camphorylsulfonyl)oxaziridines has recently been reported.10
8477proposed coordination behavior of the respective macrocycles in solution. Namely, the coordination or otherwise of the ether functions in the solid Zn(I1) and Cd(I1) complexes occurs in a directly analogous manner to their proposed interaction with these ions in solution.CdN3 unit with a "ruffled" 02N3 arrangement (Figure 2c).
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...
recommend the procedures of Table I1 using allyloxycarbonyl chloride (AOCC1) or allyl l-benzotriazoylcarbonate (AOCOBT) (23): where choice of the base and solvent is important for obtaining satisfactory yields.The AOC group is also employable for the sugarhydroxyl p r o t e c t i~n .~,~ The 0-allyloxycarbonylated nucleoside 8 was prepared in 95% yield by tert-butylmagnesium chloride (2 equiv) aided reaction of cytidine nucleoside 13 (1 equiv) and the AOC agent 22 (1.2 equiv). When this 0-AOC nucleoside was treated with a catalytic amount of Pd[P(C6H5)3]4 in the presence of HCOOH/n-C4H,NH2 (2 equiv each) for 1 h, 13 was brought back. Conveniently, the Pd(0)-catalyzed reaction of the N,Obis(allyloxycarbony1ated) derivative 5 removed contemporaneously both protections to afford the nucleoside 7 in quantitative yield.Internucleotide linkage is protectable by allyl group.1° The above described characteristic properties of AOC, coupled with the phosphite method using allyl phosphorodichloridite, enabled us to open an extremely convenient way to dinucleoside phosphates. The key operation here is complete deprotection of fully-protected dinucleoside phosphotriester intermediates by single treatment with Pd(0) catalyst. Thus, collidine-assisted (4.6 equiv) condensation of the 3'-O-unprotected thymidine nucleoside 21 (2 equiv), CH2=CHCH20PC12 (2 equiv), and the 5'-0free adenosine 6 (1 equiv) followed by NO2 oxidation (THF, -78 "C) afforded the protected TpA 24 in 80% yield. When 24 was treated with a mixture of Pd[P(c6-)3]4 and P(C6H5)3 (5 and 20 mol %/allyl), formic acid (10 equiv), and butylamine (10 equiv) in THF at room temperature for 30 min, the four allylic protecting groups were removed all at once from the nucleoside base, sugar hydroxyl, and internucleotide bond to give TpA (25) in 97% yield. In summary, the AOC group acts as both specific and general protectors. This method is useful in view of mildness of the deprotection conditions and simplicity of the workup, providing a powerful tool in nucleotide synthesis. Supplementary Material Available: Experimental details(16 pages). Ordering information is given on any current masthead page.(7) We are grateful to Hodogaya Chemicals, Co., for the generous gift of allyloxycarbonyl chloride.(8) AOCOBT (23), mp 107-111 "C, was prepared by the triethylamine-promoted (1 equiv) reaction of AOCCl (22) (1 equiv) and 1hydroxybenzotriazole (1 equiv) in THF at room temperature for 10 min. (9) Guibe, F.; MLeux, Y. S. Tetrahedron Lett. 1981, 22, 3591. (IO) Hayakawa, Y.; Uchiyama, M.; Kato, H.; Noyori, R. Tetrahedron Lett. 1985, 26, 6505.Summary: The first asymmetric oxidation of ester and amide lithium enolates 5 to optically active a-hydroxy carbonyl compounds 6 is reported using new, easily prepared, stable (camphorylsulfony1)oxaziridines (+)-(2R,8&)-3 and (-)-(2S,8&)-4. Either enantiomer of 6 can be readily obtained because the configuration of the oxaziridine three-membered ring determines the product stereochemistry.Sir: Optically active a-hydroxy carbonyl compounds are ver...
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