Asymmetric Sommelet-Hauser rearrangement of N-benzylic ammonium salts

Angewandte Chemie - International Edition

Volumn 46, Issue 46, 2007, Pages 8869-8871

  Tayama, Eiji ^a   Kimura, Hiroshi ^a  

^a NIIGATA UNIVERSITY   (Japan)

Author keywords

Amino acids; Ammonium salts; Asymmetric synthesis; Diastereoselectivity; Rearrangement

Indexed keywords

ALCOHOLS; AMINO ACIDS; ESTERS; STEREOSELECTIVITY; SYNTHESIS (CHEMICAL);

BENZYLIC AMMONIUM SALTS; DIASTEREOSELECTIVITY;

AMMONIUM COMPOUNDS;

EID: 36749099357     PISSN: 14337851     EISSN: None     Source Type: Journal    
DOI: 10.1002/anie.200703832     Document Type: Article

References (30)

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11. Previous examples of asymmetric Sommelet-Hauser rearrangements: a) S. Hanessian, C. Talbot, P. Saravanan, Synthesis 2006, 723-734:
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15. 4, THF, 0°C to RT, 85 % yield. Only one tert-butyl ester on the aromatic ring was reduced. For more details, see the Supporting Information.
16. 3CN, RT; Ts = toluene-p-sulfonyl. For more details, see the Supporting Information.
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24. To confirm that the selectivity is determined in the rearrangement step, we carried out the reaction of 4a using a lower amount of tBuOK (0.50 equiv). The rearrangement product 5a was obtained in 45% yield with a similar diastereoselectivity (25/2R = 98:2).
25. 1H NMR analysis of the diastereomer mixture of 5a showed two singlet peaks of the α proton (δ = 3.46 ppm for the 25 isomer, δ = 4.02 ppm for the 2R isomer).
26. 2 and 50% aqueous KOH (volume ratio 2:1) at 0°C for 1 h, the corresponding [1,2] Stevens rearrangement product was obtained as a major product (49% yield, d.r. = 4:1) with a small amount of 5a (4% yield, 2S/2R = 1.5:1). The mechanistic origin of the competition of Sommelet-Hauser and [1.2] Stevens rearrangement is unclear at present; further studies are necessary.
27. When the product 5b (2S/2R = 97:3) was treated with tBuOK (0.2 equiv) in THF at -40°C for 4 h, 5b was recovered in 96% yield, and the diastereomeric ratio was changed to 2S/2R = 85:15. The diastereomer mixture was treated with tBuOK (0.2 equiv) at -60°C for 8h, and 5b was recovered in 90% yield with the same diastereomeric ratio (2S/2R = 85:15).
28. -3 5M HCl));
29. see: b) C. Mellin-Morlière. D. J. Aitken, S. D. Bull, S. G. Davies, H. P. Husson, Tetrahedron: Asymmetry 2001, 12, 149-155. For more details, see the Supporting Information. (Chemical Equation Presented)
30. 2O, reflux) gave (S)-2-(dimethylamino)-2-(2-methylphenyl)ethanol in 87% yield without racemization. For more details, see the Supporting Information.