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Communication
for other multi-component reactions is currently ongoing and
will be disclosed in due course.
Table 3 Catalyst recycling in the visible-light mediated multi-component
reactiona
Cycle
1
2
3
4
5
Yield of 3a (%)
74
79
72
83
78
Experimental
General procedure for the heterogeneous photocatalyzed Ugi
type multi-component reaction
a Reaction conditions: 1a (1 mmol), 2a (0.5 mmol), H2O (10 equiv.),
P25 TiO2 (1. equiv.), 3 mL of dioxane, irradiation with a 11 W
fluorescent lamp from 3 cm distance for 4 days, yields after column
chromatography.
In a vial TiO2 (P25) (12 mg, 0.15 mmol), amine 1 (0.3 mmol),
isocyanide 2 (0.15 mmol) and H2O (27 μL, 1.5 mmol) were dis-
solved in 1 mL of dioxane. The reaction mixture was stirred
under irradiation with an 11 W fluorescent lamp (distance
approx. 3 cm). After the reaction was complete the solvent was
removed under reduced pressure and the crude mixture was
directly charged on silica gel and purified by column chromato-
graphy (cyclohexane–EtOAc 8 : 2 to 6 : 4) to afford the corres-
ponding α-amino amide 3.
Notes and references
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Chem. Rev., 2002, 102, 3811; (d) X. Chen and S. S. Mao,
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J. Photochem. Photobiol., C, 2008, 9, 157.
Fig. 1 HR-TEM and TEM analyses of TiO2 before use (top) and after use
(bottom).12
2 (a) N. Hoffmann, Chem. Rev., 2008, 108, 1052; (b) K. Zeitler,
Angew. Chem., Int. Ed., 2009, 48, 9785; (c) T. P. Yoon,
M. A. Ischay and J. Du, Nat. Chem., 2010, 2, 527;
(d) J. M. R. Narayanam and C. R. J. Stephenson, Chem. Soc.
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3 (a) M. R. Hoffmann, S. T. Martin, W. Y. Choi and
D. W. Bahnemann, Chem. Rev., 1995, 95, 69;
(b) A. Fujishima, X. T. Zhang and D. A. Tryk, Surf. Sci. Rep.,
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4 (a) M. Zhang, C. Chen, W. Ma and J. Zhao, Angew. Chem.,
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V. Loddo, G. Marcì, G. Palmisano, L. Palmisano and
S. Yurdakal, Chem.–Eur. J., 2008, 14, 4640; (d) M. Zhang,
Q. Wang, C. Chen, L. Zang, W. Ma and J. Zhao, Angew.
Chem., Int. Ed., 2009, 48, 6081; (e) S. Yurdakal,
G. Palmisano, V. Loddo, O. Alagöz, V. Augugliaro and
L. Palmisano, Green Chem., 2009, 11, 510; (f) Q. Wang,
M. Zhang, C. Chen, W. Ma and J. Zhao, Angew. Chem., Int.
Ed., 2010, 49, 7976; (g) V. Augugliaro and L. Palmisano,
ChemSusChem, 2010, 3, 1135; (h) G. Palmisano, E. Garcia-
López, G. Marcì, V. Loddo, S. Yurdakal, V. Augugliaro and
L. Palmisano, Chem. Commun., 2010, 46, 7074;
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N. Ichikuni, S. Tanaka and T. Hirai, Chem.–Eur. J., 2011, 17,
9816.
Scheme 2 Proposed reaction mechanism for the photoredox multi-com-
ponent reaction catalyzed by TiO2.
generating C. Finally, C tautomerizes to the corresponding
amide, affording product 3.
In summary, we have developed a new protocol for the syn-
thesis of α-amino amides driven by visible-light catalysis and
using cheap, robust, readily available and recyclable titanium
dioxide. The advantage of using such a heterogeneous catalyst
is the simplicity of its recycling and reuse. Thus, the protocol
presented is both environmentally acceptable and economical.
Further investigation into the applicability of this methodology
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