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0037016473
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Syntheses based on vicinal anion of (-)-dimenthyl succinate, see:
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34
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2342564520
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note
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Treatment of 1a with 1 equiv of LDA, followed by reacting with 1 or 2 equiv of benzyl bromide under the standard conditions provided a low yield of the expected product 3a
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35
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84987564680
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note
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1H NMR and MS. In spite of these results, it was still assumed that the vicinal dianion 2a was generated under the conditions described. This may be due to a strong H-bonded complex between diisopropylamine and the dilithiated derivative. Such interaction effecting incomplete deuteration of the generated lithium derivative was reported by Seebach (Laube, T.; Dunitz, J. D.; Seebach, D. Helv. Chim. Acta, 1985, 68, 1373-1393). The reaction of the vicinal dianion 2a with 2.2 equiv of benzyl bromide at -78°C to room temperature overnight (12-16 h) afforded dibenzylated product 9 in 20-30% yields together with 30-40% yields of the chiral auxiliary, (4S, 5R)-(+)-1, 5-dimethyl-4-phenyl-2-imidazolidinone and compound 11. The formation of 9 supported the presence of the vicinal dianion 2a. Compound 9 was obtained as a single diastereomer and its structure is proposed as shown below. The results also indicated that the vicinal dianion 2a slowly decomposed during warming from -78°C to rt to provide 10 and 11.
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37
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2342463712
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note
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2 using SHELXL-97 to give a final R -factor of 0.0493 and wR=0.1130 (all data). Atomic coordinates, bond lengths, bond angles, and thermal parameters have been deposited with the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, ENGLAND (CCDC 216625)
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38
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0034723338
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and references cited therein
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Kise N., Ueda T., Kumuda K., Terao Y., Ueda N. J. Org. Chem. 65:2000;464-468. and references cited therein
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J. Org. Chem.
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Kise, N.1
Ueda, T.2
Kumuda, K.3
Terao, Y.4
Ueda, N.5
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39
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2342516877
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note
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The chiral auxillary was recovered in 85-95% yields and could be reused without loss of diastereoselectivity
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40
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2342637843
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note
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3)
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