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3
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0007378437
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The stereochemical assignment of the enantiomers of omeprazole is described in von Unge, S.; Langer, V.; Sjolin, L. Tetrahedron: Asymmetry 1997, 8, 1967-1970.
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4
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0007423208
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The enantiomers of omeprazole have previously been isolated by resolution procedures, see: (a) Erlandsson, P.; Isaksson, R.; Lorentzon, P.; Lindberg, P. J. Chromatogr. 1990, 532, 305-319. (b) Kohl, B.; Senn-Bilfinger, J. Patent appl. DE 4035455 (Priority date: November 8, 1990). (c) Lindberg, P.; von Unge, S. Patent appl. WO 94/27988 (Priority date: May 28, 1993).
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5
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0007377355
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Sulphide 1 is a key intermediate in the production of racemic omeprazole. The synthesis of 1 is described in Carlsson, E. I.; Junggren, U. K.; Larsson, H. S.; von Wittken Sundell, G. W. Patent appl. EP 074341. (Priority date: August 13, 1981).
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6
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0007423379
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(a) Davis, F. A.; Sheppard, A. C. Tetrahedron 1989, 45, 5703-5742. (b) Davis, F. A.; Reddy, R. T.; Weismiller, M. C. J. Am. Chem. Soc. 1989, 111, 5964-5965. (c) Davis, F. A.; Reddy, R. T.; Han, W.; Carroll, P. J. J. Am. Chem. Soc. 1992, 114, 1428-1437.
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7
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0007454828
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The chiral oxidant used was (3'S,2R)-(-)-N-(phenylsulphonyl)-(3,3-dichlorocamphoryl)oxaziridine. Its synthesis is described in Ref. 6c.
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8
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0007428749
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von Unge, S. Patent appl. WO 97/02261 (Priority date: July 3, 1995).
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9
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0007418698
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For recent reviews see: (a) Kagan, H. B.; Diter, P. Organosulfur Chem. 1998, 2, 1-39. (b) Kagan, H. B. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; Wiley-VCH: New York, 2000; Chapter 6C, pp. 327-356.
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10
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0007451358
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4, DET and t-BuOOH in the absence of water but by increasing the amount of DET; see: (c) Di Furia, F.; Modena, G.; Seraglia, R. Synthesis 1984, 325-326.
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11
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0007417632
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(a) Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1980, 102, 5974-5976. (b) Rossiter, B. E.; Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1981, 103, 464-465.
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12
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0007418699
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Kagan and co-workers have for instance demonstrated that the enantiomeric excess for p-tolyl methyl sulphoxide is dramatically decreased when less than 50 mol% of Ti-catalyst is being used (see Ref. 10b).
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13
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0007452029
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As opposed to the allylic alcohols employed in the Sharpless asymmetric epoxidation procedure, prochiral sulphides employed in asymmetric sulphoxidations using a modified Sharpless reagent are considered to be non-functional substrates. Thus, the enantioselectivity in these reactions is regarded to be derived mainly from the steric effects of the prochiral sulphide, i.e. by having a large difference in the size of the substituents attached to sulphur; see: (a) Kagan, H. B.; Rebiere, F. Synlett 1990, 643-650. (b) Pitchen, P.; France, C. J.; McFarlane, I. M.; Newton, C. G.; Thompson, D. M. Tetrahedron Lett. 1994, 35, 485-488. (c) Pitchen, P. Chem. Ind. 1994, 636-639.
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14
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0007416513
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Chemists at Hoffmann-La Roche have reported that Kagan's original method indeed could be used for the synthesis of the enantiomers of the omeprazole analogue Ro 18-5364 with a modest enantiomeric excess of the crude product (30%); see: Sigrist-Nelson, K.; Krasso, A.; Muller, R. K. M.; Fischli, A. E. Eur. J. Biochem. 1987, 166, 453-459. However, we were not able to reproduce this result in this study (see: Ref. 15).
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15
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0007452030
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For further experimental procedures, see: Larsson, E. M.; Stenhede, U. J.; Sorensen, H.; von Unge, P. O. S.; Cotton, H. K. Patent appl. WO 96/02535 (Priority date: July 15, 1994).
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16
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0007428750
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4, DET and water is necessary in order to ensure high ee's in asymmetric oxidations of different sulphides; see: (a) Diter, P.; Samuel, O.; Taudien, S.; Kagan, H. B. Tetrahedron: Asymmetry 1994, 4, 549-552. (b) Brunel, J.-M.; Diter, P.; Duetsch, M.; Kagan, H. B. J. Org. Chem. 1995, 60, 8086-8088.
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17
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0007417586
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The choice of solvent has been reported earlier to have a pronounced influence on the enantiomeric excess of sulphoxides obtained by Kagan's original method; see e.g.: Kagan, H. B.; Dunach, E.; Nemecek, C.; Pitchen, P.; Samuel, O.; Zhao, S.-H. Pure Appl. Chem. 1985, 57, 1911-1916.
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18
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0007423209
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In general, a temperature lower than -20°C during the asymmetric oxidation of sulphides by Kagan's method has proven to be beneficial for the enantioselectivity (see Ref. 13a).
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