Aqueous 30% H 2 O 2 in hexafluoro-2-propanol (HFIP) is carbon double bond are shown to not be affected by the reagent system used. The oxidation of glycosyl sulfides to described as a facile, selective and efficient oxidant for the conversion of sulfides to sulfoxides under neutral conditions. glycosyl sulfoxides was achieved in very high yield at room temperature. The nitrogen center of the pyridine molecule and the carbon-
Results and Discussionin a very short reaction time. The substituents on the phenyl group had no significant effect on the reaction: With elec-In our search for new low-cost and environmental tron-donating p-methyl, p-chloro substituents (1h and 1i) friendly oxidizing systems, we have recently reported on the and with a strong electron-withdrawing group like p-nitro Mn(OAc)3·2H2O catalyzed aerobic oxidation of olefins. [9a] (1j) the reaction occurred smoothly to give the correspond-However, this system was not selective in sulfide oxidation, ing sulfoxides 2h؊j in excellent yields. leading to a mixture of sulfoxide and sulfone. [9b] We thus Table 1. Oxidation of sulfides RϪSϪR* with aqueous 30% H 2 O 2 turned to oxidation reactions involving 30% aqueous H 2 O 2 in HFIP [a] as the most readily available inexpensive oxidant. The use of a fluorous phase has recently been proved to present several Substrate R RЈ Time [min] Product Yield (%) [b] advantages in organic syntheses, [10] and considering the high efficiency of protic solvents for oxidation of sulfide 1a nBu nBu 5 2a 92 1b PhCH 2 PhCH 2 5 2b 98 with aqueous H 2 O 2 , we chose 1,1,1,3,3,3-hexafluoro-2-pro-1c tBu tBu 20 2c 97 panol (HFIP) (pK ϭ 9.3) [11] as a fluorous alcoholic solvent. 1d ϪC 4 H 8 Ϫ 5 2d 82 The oxidation of ethyl phenyl sulfide was carried out in 1e Ph Et 5 2e 97 1f Ph PhCH 2 5 2f 97 HFIP with aqueous 30% H 2 O 2 at room temp., and after 30 1g Ph Ph 5 2g 99 min afforded the corresponding ethyl phenyl sulfoxide as 1h p-MeC 6 H 4 Me 5 2h 98 the only product in an excellent yield (97%). The sulfoxide 1i p-ClC 6 H 4 Me 5 2i 95 1j p-O 2 NC 6 H 4 Me 10 2j 92 was recovered in HFIP which was further distilled and reused. The sulfoxide was recovered in the HFIP phase after [a] Sulfide (2 mmol), aqueous 30% H 2 O 2 (4 mmol), HFIP (2.5 ml). quenching the reaction with satd. sodium sulfite solution. Ϫ [b] Isolated yields.The fluorous solvent (HFIP) can be recovered by distillation. Prolonging the reaction to 3 h did not give any sul-We then investigated the stability of sensitive functionalities under these oxidation conditions. Cyclopropyl phenyl fone. With an excess of aqueous 30% H 2 O 2 at room temp., ethyl phenyl sulfoxide was formed within 5 min. When ethyl sulfide (3) gave cyclopropyl phenyl sulfoxide (4) without affecting the strained cyclopropyl group (see Table 2). Allylic phenyl sulfoxide was allowed to react with 30% aqueous H 2 O 2 in HFIP at 25°C, the starting sulfoxide was reco-sulfides 5 and 7, terminal olefinic sulfide 9 and vinylic sulfide 11 afforded the corresponding sulfoxides in high yields vered unchanged.The...
Aqueous 30% H2O2 in hexafluoro‐2‐propanol (HFIP) is described as a facile, selective and efficient oxidant for the conversion of sulfides to sulfoxides under neutral conditions. The nitrogen center of the pyridine molecule and the carbon–carbon double bond are shown to not be affected by the reagent system used. The oxidation of glycosyl sulfides to glycosyl sulfoxides was achieved in very high yield at room temperature.
A series of isodeoxypodophyllotoxin (5) analogues, 26-38, with various isoprene-derived side chains at the E-ring were designed and synthesized. For comparison, compound 39, with a benzyloxy group on the E-ring, and six D-ring opened analogues, 40-45, were also prepared. All the synthetic compounds were evaluated for their cytotoxic activities in vitro against seven cultured human tumor cell lines. Compounds 27, 43, and 44 were more cytotoxic than etoposide on BEL-7404, A549, and HL-60 cell lines, respectively. However, none of the synthetic isodeoxypodophyllotoxins were more cytotoxic than podophyllotoxin (1).
The minimum fluidization behavior of four different binary particle systems with different Geldart classification is experimentally investigated by carrying out slow defluidization of an experimental cold device of I.D. 300 mm and height 3 m. The solid particles are four kinds of quartz sand particles with equal density, corresponding to Group A, B, C and D particles of Geldart classification, respectively. The fluidization processes can be divided into packing state, partial fluidization state and complete fluidization state. The difference in physical properties and mass fraction of the two constituent solid phases is found to strongly influence the fluidization behavior and the minimum fluidization velocity during the slow defluidization process. For binary particle systems, the minimum fluidization velocity decreases with increasing mass fraction of the component whose fluidization quality is better. Finally, the models of Noda et al. (1986), Cheung et al. (1974) and Chiba et al. (1979) are used to predict the minimum fluidization velocity of above binary particle systems.
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