Enantioselective organocatalytic diels aminations: α-aminations of cyclic β-keto esters and β-keto lactones with cinchonidine and cinchonine

Synlett

Volumn , Issue 12, 2004, Pages 2115-2118

  Pihko, Petri M ^a   Pohjakallio, Antti ^a  

^a AALTO UNIVERSITY   (Finland)

Author keywords

keto esters; Animations; Cinchona alkaloids; Enantioselectivity; Organocatalysis

Indexed keywords

AZO COMPOUND; BETA KETO LACTONE; CINCHONA ALKALOID; CINCHONIDINE; CINCHONINE; CYCLIC BETA KETO ESTER; DIBENZYL AZODICARBOXYLATE; DICARBOXYLIC ACID; ESTER; LACTONE; UNCLASSIFIED DRUG;

ALPHA AMINATION; AMINATION; ARTICLE; CATALYSIS; DIELS AMINATION; ENANTIOSELECTIVITY; QUANTUM YIELD; REACTION ANALYSIS;

EID: 5644247697     PISSN: 09365214     EISSN: None     Source Type: Journal    
DOI: 10.1055/s-2004-831326     Document Type: Article

References (21)

1. (a) Diels, O. Liebigs Ann. Chem. 1922, 429, 1.
2. (b) Diels, O.; Behncke, H. Chem. Ber. 1924, 57, 653.
3. (c) See also: Huisgen, R.; Jakob, F. Liebigs Ann. Chem. 1954, 590.
4. (d) For a recent review of asymmetric electrophilic α-aminations of carbonyl compounds, see: Greck, C.; Drouillat, B.; Thomassigny, C. Eur. J. Org. Chem. 2004, 1377.
5. (a) Marigo, M.; Juhl, K.; Jørgensen, K. A. Angew. Chem. Int. Ed. 2003, 42, 1367.
6. (b) For a related auxiliary-controlled α-amination reaction using a Ru catalyst, see: Lumbierres, M.; Marchi, C.; Moreno-Mañas, M.; Sebastián, R. M.; Vallribera, A.; Lago, E.; Molins, E. Eur. J. Org. Chem. 2001, 2321.
7. (a) List, B. J. Am. Chem. Soc. 2002, 124, 5656.
8. (b) Bøgevig, A.; Juhl, K.; Kumaragurubaran, N.; Zhuang, W.; Jørgensen, K. A. Angew. Chem. Int. Ed. 2002, 41, 1790.
9. (c) Vogt, H.; Vanderheiden, S.; Bräse, S. Chem. Commun. 2003, 2448.
10. Kumaragurubaran, N.; Juhl, K.; Zhuang, W.; Bøgevig, A.; Jørgensen, K. A. J. Am. Chem. Soc. 2002, 124, 6254.
11. (a) During the preparation of this manuscript, Jørgensen and co-workers reported a similar approach to α-aminations of β-keto esters using a quinidine-derived β-isocupreidine catalyst: Saaby, S.; Bella, M.; Jørgensen, K. A. J. Am. Chem. Soc. 2004, 126, 8120.
12. (b) With substrates 1 and 5, the enantioselectivities obtained with cinchonine were similar to those obtained by Jørgensen with di-tert-butyl azodicarboxylate for similar substrates; however, the reaction rates were much faster in the present study.
13. 2 afforded the recovered catalyst in quantitative yield and >90% purity.
14. The racemic samples were prepared either with KOAc catalyst or by a mixing the cinchonine- and cinchonidine-derived products.
15. minor = 124 min.
16. In addition to 3, α-methyl, α-benzyl and α-allyl- substituted ethyl acetoacetates were also screened as substrates, all affording the products in good yields (70-85%) but poor enantioselectivity (<35% ee).
17. Compound 4 was readily prepared by transesterification from 1 (BnOH, 175 °C). See: Taniguchi, M.; Koga, K.; Yamada, S. Chem. Pharm. Bull. 1972, 20, 1438.
18. Compounds 7 and 8 were obtained by acylation of γ-butyrolactone [LDA, THF, -78 °C, then isobutyroyl chloride (7) or pivaloyl chloride (8)].
19. Brown, H. C.; Brewster, J. H.; Shechter, H. J. Am. Chem. Soc. 1954, 76, 467.
20. Hoffmann, R. W. Chem. Rev. 1989, 89, 1841.
21. Control experiments with 20 mol% 6-methoxyquinoline and quinoline showed that these alone are poor catalysts for the reaction. Presumably, both the basic amine moiety and the free OH group are required for effective catalysis. Studies are in progress to determine the full mechanistic picture of these reactions.