Organic Letters
Letter
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Scheme 5. Control Experiments
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Scheme 6. Rational Hypothesis of the Cyclic Anti-
Azacarboxylation Reaction
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different indole-3-carboxylic acids. The reaction was conducted
with ZnEt2 under a balloon atmosphere of carbon dioxide and no
transition metal catalyst is necessary. Functional groups including
ester, cyano, nitro, acetyl, −OH, −NHTs, trifluoromethyl, etc.
were smoothly tolerated, and the potential has been demon-
strated by applying it to the synthesis of Lotronex. This protocol
should be easily applicable to the synthesis of the targets listed in
Figure 1. Thus, such a mild carbon dioxide reaction may provide
an efficient entry to the library of bioactive compounds due to the
easily available and diversified nature of the starting compounds.
Such syntheses, including those of pravadoline, AM630, PD
molecules, and their derivatives, by using this CO2-based
carboxylation reaction are being actively pursued by our group.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
Experimental procedures, analytical data, and NMR
spectra of the products (PDF)
(8) For noncatalyzed reaction of organozinc compounds with CO2,
see: (a) Kobayashi, K.; Kondo, Y. Org. Lett. 2009, 11, 2035. (b) Miao, B.;
Ma, S. Org. Chem. Front. 2015, 2, 65. (c) Miao, B.; Li, G.; Ma, S. Chem. -
Eur. J. 2015, 21, 17224.
AUTHOR INFORMATION
Corresponding Author
■
(9) (a) Ishida, T.; Kikuchi, S.; Tsubo, T.; Yamada, T. Org. Lett. 2013, 15,
848. (b) Ishida, T.; Kikuchi, S.; Yamada, T. Org. Lett. 2013, 15, 3710.
(10) (a) Whitehead, J. W. F.; Mills, K.; Coates, I. H.; Oxford, A. W.;
North, P. C. US005196534A, 1993. (b) Coates, I. H.; Oxford, A. W.;
North, P. C.; Tyers, M. B. US005221687A, 1993. (c) Cooper, S. J.;
Coates, I. H.; Oxford, A. W.; North, P. C. US005221687A, 1993.
(d) Prakash, S. R.; Cable, K. M.; Correa, I. D.; Fellows, I.; Montgomery,
S.; Newman, J. J.; Waterhouse, I.; Wells, G. N.; Sutherland, D. R. J.
Labelled Compd. Radiopharm. 1995, 36, 993. (e) Mills, K.; Coates, I. H.;
Oxford, A. W.; North, P. C. EP 0458624A1, 1991. (f) Coates, I. H.;
North, P. C.; Oxford, A. W. EP 0306323A2, 1988. (g) North, P. C.;
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the National Natural Science Foundation
of China (21232006) and the National Basic Research Program
of China (973 Program) (No. 2015CB856600) is greatly
appreciated. We thank Yang Tang in this group for reproducing
the results of 2c and 2y in Table 3 and 8 in Scheme 2.
(12) (a) Nakamura, M.; Ilies, L.; Otsubo, S.; Nakamura, E. Angew.
Chem., Int. Ed. 2006, 45, 944. (b) Nakamura, M.; Ilies, L.; Otsubo, S.;
Nakamura, E. Org. Lett. 2006, 8, 2803. (c) Yin, Y.; Ma, W.; Chai, Z.;
Zhao, G. J. Org. Chem. 2007, 72, 5731. (d) Okuma, K.; Seto, J.;
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