Table 4 Deprotection to free-primary amines
3 DRA of ammonia with aldehydes: only example available to give
free terminal primary amines: T. Gross, A. M. Seayad, M. Ahmad
and M. Beller, Org. Lett., 2002, 4, 2055.
4 Reductive amination of ammonia with aldehydes gave only secondary
amines: B. Miriyala, S. Bhattacharyya and J. S. Williamson, Tetra-
hedron, 2004, 60, 1463.
3 or 6
Conditions
t/h
12 (conversions)a
5 For recent examples of DRA using catalytic hydrogenation: S. Fleischer,
S. Zhou, K. Junge and M. Beller, Chem.–Asian J., 2011, 6, 2240.
6 For recent examples of DRA using active borane based reducing
agents: (a) M. Taibakhsh, R. Hosseinzadeh, H. Alinezhad,
S. Ghahari, A. Heydari and S. Khaksar, Synthesis, 2011, 490;
(b) M. Tokizane, K. Sato, Y. Sakami, Y. Imori, C. Matsuo,
T. Ohta and Y. Ito, Synthesis, 2010, 36.
7 For recent examples of DRA using transfer hydrogenation
from Hantzsch ester: (a) R. I. Storer, D. E. Carrera, Y. Ni and
D. W. C. MacMillan, J. Am. Chem. Soc., 2006, 128, 84;
(b) M. Zhang, H. Yang, Y. Zhang, C. Zhu, W. Li, Y. Cheng and
H. Hua, Chem. Commun., 2011, 47, 6605.
1
2
3
3a
6a
6b
A
B
C
6
1
2
Quantitative
Quantitative
Quantitative
A: in 6 N HCl solution, reflux; B: in 20% CF3CO2H in CH2Cl2, rt;
a
C: 20% piperidine in DMF, rt. Conversions were determined by
1H NMR spectroscopy using acetophenone as an internal standard.
8 For recent examples of DRA using transfer hydrogenation from
formates: (a) D. O’Connor, A. Lauria, S. P. Bondi and S. Sabaet,
Tetrahedron Lett., 2011, 52, 129; (b) C. Wang, A. Pettman, J. Basca
and J. Xiao, Angew. Chem., Int. Ed., 2010, 49, 7548.
9 For recent examples of DRA using transfer hydrogenation from
alcohols: (a) D. Gnanamgari, A. Moores, E. Rajaseelan and
R. H. Crabtree, Organometallics, 2007, 26, 1226; (b) F. Alonso,
P. Riente and M. Yus, Synlett, 2008, 1289.
10 DRA using transfer hydrogenation using organosilanes: using
trifluoroacetic acid (TFA)–polymethylhydrosiloxane (PMHS):
(a) J. P. Patel, A.-H. Li, H. Dong, V. L. Korlipara and
M. J. Mulvihill, Tetrahedron Lett., 2009, 50, 5975; using
Ti(OiPr)4–Et3SiH: (b) S. Chandrasekhar, C. R. Reddy and
M. Ahmed, Synlett, 2000, 1655; (c) D. Menche, F. Arikan, J. Li
and S. Rudolph, Org. Lett., 2007, 9, 267; using Bu2SnCl2–PhSiH3:
(d) J. J. Kangasmetsa and T. Johnson, Org. Lett., 2005, 7, 5653; using
InCl3–PhSiH3: (e) O.-Y. Lee, K.-L. Law and D. Yang, Org. Lett.,
2009, 11, 3302; using MoO2Cl2–PhSi3: (f) C. A. Smith, L. E. Cross,
K. Hughes, R. E. Davis, D. B. Judd and A. T. Merritt, Tetrahedron
Lett., 2009, 50, 4906; using Ga(OTf)3–Et3SiH: (g) G. K. S. Prakash,
C. Do, T. Mathew and G. A. Olah, Catal. Lett., 2010, 137, 111; using
oxo-rhenium(V)–Et3SiH: (h) S. C. A. Sousaa and A. C. Fernandesa,
Adv. Synth. Catal., 2010, 352, 2218.
11 (a) G. Li, Y. Liang and J. C. Antilla, J. Am. Chem. Soc., 2007,
129, 5830; (b) C. Li, C. Wang, B. Villa-Marcos and J. Xiao, J. Am.
Chem. Soc., 2008, 130, 14450; (c) L. C. Misal Castro, J.-B. Sortais
and C. Darcel, Chem. Commun., 2012, 48, 151.
12 Only examples dealing with reductions of preformed imines with
electron-deficient protecting groups: (a) K. A. Nolin, R. W. Ahn
and F. D. Toste, J. Am. Chem. Soc., 2005, 127, 12462;
(b) K. A. Nolin, R. W. Ahn, Y. Kobayashi, J. J. Kennedy-Smith
and F. D. Toste, Chem.–Eur. J., 2010, 16, 9555.
Scheme 3 Reduction followed by substitution vs. DRA.
Finally, the easy de-protection of synthesized protected amines
was carried out to provide free primary amines (see Table 4).
To gain further insight into the mechanism of this Re2O7
catalysis, we performed the following reactions. As shown in
Scheme 3, under these conditions, the current reaction proceeded
through the reductive-amination pathway (e.g., formation of imine,
followed by reduction using in situ formed [H-Re] species12,16) only,
not via reduction followed by the substitution process.
In conclusion, we have reported that the Re2O7-catalyst is
capable of promoting the reductive amination of electron-
deficient amines with aldehydes. The reaction proceeded in an
excellent chemo- and regio-selective manner. The sequential
and cascade reductive amination–conjugate addition to provide
derivatives of isoindoline, containing a chiral center, has also
been exemplified. Finally, the easy deprotection of the corre-
sponding products to free terminal primary amines has also
been carried out. Further utilization of oxo-rhenium com-
plexes for reductive amination of ketones is in progress.
P.G. thanks the DST, India, for a research grant and
Dr Deepak Chopra for useful discussions. B.G.D. thanks
the CSIR, New Delhi, for a fellowship. We are thankful to
SID, IISc Bangalore, for providing us an opportunity
to perform ICP-OES experiments. We are also thankful to
Shubhadip Chakraborty, IISc Banglore for his help.
13 T. W. Greene and P. G. M. Wuts, Protective Groups in Organic
Synthesis, Wiley, New York, 3rd edn, 1999.
14 Usually involves multistep protocols, for details see: (a) M. Yus,
J. C. Gonzalez-Gomez and F. Foubelo, Chem. Rev., 2011,
´ ´
111, 7774; (b) W. Yan, D. Wang, J. Feng, P. Li, D. Zhao and
R. Wang, Org. Lett., 2012, 14, 2512.
15 (a) S. Pramanik and P. Ghorai, Chem. Commun., 2012, 48, 1820;
(b) B. G. Das, R. Nallagonda and P. Ghorai, J. Org. Chem., 2012,
77, 5577.
16 (a) M. R. Luzung and F. D. Toste, J. Am. Chem. Soc., 2003,
125, 15760; (b) E. A. Ison, E. R. Trivedi, R. A. Corbin and
M. M. Abu-Omar, J. Am. Chem. Soc., 2005, 127, 15374.
17 (a) R. Hua and J.-L. Jiang, Curr. Org. Synth., 2007, 4, 151;
(b) P. Ghorai and P. H. Dussault, Org. Lett., 2009, 11, 213;
(c) S. Bellemin-Laponnaz, ChemCatChem, 2009, 1, 357; (d) A. T.
Herrmann, T. Saito, C. E. Stivala, J. Tom and A. Zakarian, J. Am.
Chem. Soc., 2010, 132, 5962; (e) I. Volchkov, S. Park and D. Lee,
Org. Lett., 2011, 13, 3530.
18 Different sources of Re2O7 as well as different purity levels
provided the similar reactivity (see ESIw).
19 The trace analysis of Re2O7 using the ICP-OES technique, the major
contaminants detected [ppm]: Co (0.14), Cu (0.72), Fe (3.7). But, the
current DRA using ppm level of these catalysts (such as CoCl2, CuBr2,
and FeCl3) in the absence of Re2O7 was not positive. This ruled out the
possibility of current catalysis by trace impurities in Re2O7.
Notes and references
1 (a) S. A. Lawrence, Amines: Synthesis, Properties and Applications,
Cambridge University Press, Cambridge, 2004; (b) K. M. Patil,
R. J. Naik, Rajpal, M. Fernandes, M. Ganguli and V. A. Kumar,
J. Am. Chem. Soc., 2012, 134, 7196.
2 (a) For review: R. P. Tripathi, S. S. Verma, J. Pandey and
V. K. Tiwari, Curr. Org. Chem., 2008, 12, 1093; (b) S. Gomez,
J. A. Peters and T. Maschmeyer, Adv. Synth. Catal., 2002,
344, 1037.
c
8278 Chem. Commun., 2012, 48, 8276–8278
This journal is The Royal Society of Chemistry 2012