2308
S. Hwang et al. / Tetrahedron Letters 50 (2009) 2305–2308
7. While this Letter is in preparation, Zhang et al. has published a communication
having similar approach for the isoquinoline synthesis. However, the
References and notes
a
demonstrated scope has not been examined with electron-deficient aromatic
substrates or for the synthesis of more elaborate heterocycles, such as 1,6-
naphthyridine or pyridoisoquinolines. Furthermore, employing TfOH as co-
catalyst, we arrived at much milder reaction conditions. See Gao, H.; Zhang, J.
Adv. Synth. Catal. 2009, 351, 85.
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Korivi, R. P.; Cheng, C.-H. Org. Lett. 2005, 7, 5179; For electrophile-induced
cyclizations, see: (h) Ishikawa, T.; Manabe, S.; Akiwa, T.; Kudo, T.; Saito, S. Org.
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AgOTf catalyzed Pictet–Spengler reaction, see: (d) Youn, S. W. J. Org. Chem.
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intermediate, see: (e) Yang, Y.-Y.; Shou, W.-G.; Chen, Z.-B.; Hong, D.; Wang,
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5. (a) Yeom, H.-S.; Lee, E.-S.; Shin, S. Synlett 2007, 2292; (b) Yeom, H.-S.; Kim, S.;
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9. The starting aldehydes were mixed with BnONH2ꢁHCl (or AllylONH2ꢁHCl,
1.1 equiv) and NaOAc (1.1 equiv) in CH2Cl2–MeOH (1:1) at rt. After 1 h, the
desired O-alkyl oximes were obtained in good yields (75–90%) after
chromatography.
10. With stoichiometric amount of electrophilic metal, M-bound intermediate (Au-
Csp2) was isolated, which proto-demetallate in the presence of acid, see (a) Liu,
L.-P.; Mashuta, M. S.; Hammond, G. B. J. Am. Chem. Soc. 2008, 130, 17642; For
examples of the use of acid co-catalyst in electrophilic metal catalysis, see: (b)
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9, 3191.
11. However, the substrate with
R
2 = n-Bu similar to 2bc led to an efficient
cyclization in 2 h as indicated by 1H NMR, although the yield was not
determined due to its volatility.
12. One limitation of the procedure using t-butylimine precursors is the
inaccessibility and/or instability of the corresponding ketimine
derivatives, and thus derivatization at C1-position of isoquinolines is
not viable (Ref. 3).
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Leopard, S. H.; Wang, J.; Peng, H.-L.; Platz, M. S.; Xue, J.; Phillips, D. L.; Glover, S.
A.; Novak, M. J. Am. Chem. Soc. 2008, 130, 16021; (b) Abramovitch, R. A.;
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Chem. Soc. 1981, 103, 4558.
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14. Durmaz, Y. Y.; Yilmaz, G.; Yagci, Y. J. Polym. Sci., Part A.; Polym. Chem. 2007, 45, 423.
15. However, in the presence of BHT, the reaction was much slower due to the
effect of phenolate counter anion.