Stereoselective α-alkylation of methyl 6-deoxy-3,4-di-O-(tert-butyldimethylsilyl)-2-O-(2-methyl-3-oxobutanoyl)-α-d-glucopyranoside

Tetrahedron Letters

Volumn 50, Issue 10, 2009, Pages 1139-1142

  Akashi, Yoko ^a   Takao, Ken ichi ^a   Tadano, Kin ichi ^a  

^a KEIO UNIVERSITY   (Japan)

Author keywords

Alkylation; Asymmetric synthesis; Carbohydrates; Chiral auxiliary; Stereoselective synthesis

Indexed keywords

CARBOHYDRATE DERIVATIVE; METHYL 6 DEOXY 3,4 DI O(TERT BUTYLDIMETHYLSILYL) 2 O(2 METHYL 3 OXOBUTANOYL) ALPHA DEXTRO GLUCOPYRANOSIDE; UNCLASSIFIED DRUG;

ALKYLATION; ARTICLE; ASYMMETRIC SYNTHESIS; BENZYLATION; CHEMICAL REACTION; CHEMICAL STRUCTURE; STEREOCHEMISTRY; SYNTHESIS;

EID: 58349101075     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2008.12.091     Document Type: Article

References (38)

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19. 4k,5
20. 13C NMR, IR, and HRMS]. Yields refer to isolated products after purification by column chromatography on silica gel.
21. +-OMe) m/z 375.2387, found 375.2382.
22. We examined this silyl-group migration using other bases. For example, 2,4-di-O-TBS derivative 8 (44%), 3,4-di-O-TBS derivative 9 (16%), and 1 (32% recovery) were obtained when LiHMDS (1.0 mol equiv) was used in THF at -78 to -20 °C. For convenient purification and high-yield of 9, we adopted the stepwise migration via the isolation of 8.
23. 3 as base. As a result, 2-O-(2-methyl-3-oxobutanoyl) derivative 11 was obtained in less satisfactory yield with concomitant production of the 2-O-(2,2-dimethyl-3-oxobutanoyl) derivative. For this reason, we prepared 11 by direct introduction of the 2-methyl-3-oxobutanoyl group at O-2 of 9 under the neutral retro-Diels-Alder strategy shown in Scheme 3.
24. Sato M., Ogasawara M., Oi K., and Kato T. Chem. Pharm. Bull. 31 (1983) 1896-1901
25. 13C NMR analysis, the diastereomeric ratio of 11 was estimated to be ca. 2:1 to 3:1. As separation of the diastereomers was fruitless, we did not determine the stereochemistry of the respective diastereomers.
26. +) m/z 544.3252, found 544.3258.
27. 1H NMR analysis.
28. +-OMe) m/z 563.3224, found 563.3242.
29. The detachment of the sugar template from 12 did not proceed under the ethanolytic conditions. We had encountered the same difficulty in the detachment of the sugar template from other α,α-dialkylated acetoacetate-derivatives; see Ref. 4k.
30. 3), see:. Fráter G. Helv. Chim. Acta 62 (1979) 2825-2828
31. The hydrazinolysis of 12 was accompanied by the hydrogenation of the allylic olefin to some extent. Thus, 12 was subjected to hydrogen addition prior to hydrazinolysis.
32. For the hydrazinolysis conditions, see:. Moreno-Mañas M., Trepat E., Sebastián R.M., and Vallribera A. Tetrahedron: Asymmetry 10 (1999) 4211-4224
33. +) m/z 154.1106, found 154.1092.
34. 2O, EtOH, 140 °C in a sealed tube.
35. 3), see Ref. 19.
36. The conditions: CHIRALPAK OD column, hexane/2-propanol = 20:1.
37. A referee suggested the participation of anomeric OMe for the potassium-chelate formation. Although we have no evidence which rules out this possibility, we insist on the presence of the chelate structure depicted in Scheme 6 by the following reason. If the potassium-chelate forms between the OMe and enolate, the sterically less-congested space might turn out to be Re-face (not the Si-face) of the α-methylated enolate.
38. 4k,5 the highly stereoselective introduction of the (S)-quaternary carbon center into the acetoacetate ester 2 could not be attained by changing the order of the addition of the electrophiles, that is, allylation (or benzylation) and then methylation.