Reusable Gold(I) Catalysts with Unique Regioselectivity
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(ꢃ2), 41.7 (43.6), 31.6 (33.8), 28.9 (31.3), 26.3 (26.8), 22.4
(22.3), 20.6, 19.1, 13.9 (13.8).
lysed conditions since it is well-reported that overre-
action of imine 7 leads to polysubstituted 1,2-dihydro-
quinolines.[13c,25] Dienylamines have not been previ-
ously obtained in an efficient manner and further
studies about the synthesis of these new products are
being carried out.
Typical Hydroamination Procedure for Internal
Alkynes (Table 4, entry 1)
Complex 1 (22 mg, 5 mol%), diphenylacetylene 14 (89 mg,
0.5 mmol) and p-toluidine
4 (53.5 mg, 0.5 mmol) were
placed into a vial. Then, CH3CN (0.25 mL) was added and
the vial was sealed. The mixture was placed in a pre-heated
oil bath at 808C and magnetically stirred for 24 h. Then, the
mixture was concentrated under reduced pressure and n-
hexanes (10 mL) added. The mixture was left into a fridge
at À148C for 4 h. The liquid was passed through a filter con-
taining a Celiteꢂ layer on top. The solid was washed with
n-hexanes and the liquid was filtered again. The filtrates
were concentrated under reduced pressure and, after drying
under vacuum the resulting residue, (1,2-diphenylethyli-
dene)-p-tolylamine 16 (E:Z=5:1) was obtained; yield:
106 mg (75%). GC/MS: major peaks found at m/z=285
Conclusions
Easy-to-make, stable gold(I) phosphine complexes 1
and 2 are regioselective catalysts for the intermolecu-
lar hydroamination of both internal and terminal al-
kynes with alkyl and aromatic amines. The obtained
regioselectivity is based on electronic rather than
steric factors, which act as descriptors of the reaction
and allow the obtention of regiosiomers not previous-
ly observed for internal alkynes. The reaction proce-
dure is simple, convenient and environmentally
friendly. The complexes can be quantitatively recov-
ered by simple precipitation in hexane and reused in
a next run. A plausible mechanism has been pro-
posed. Different tandem reactions which involve the
gold-catalysed hydroamination have been shown. The
catalytic system reported in this work is unique in
terms of reusability, mildness and versatility, and
could be useful in the synthesis of simple and more
complex products.
1
(M+), 195, 194, 91, 65; H NMR: d=7.80 (2H, dd, J=8 Hz,
2 Hz), 7.35–6.90 (10H, mult), 6.64 (2H, d, J=8 Hz), 3.97
(2H, s), 2.19 (3H, s); 13C NMR (signals corresponding to
the minor isomer between brackets): d=166.2 (165.7),
148.4, 138.4, 137.2, 133–126 (15 C), 36.0, 20.8.
Supporting Information
General methods, experimental procedures including syn-
theses and characterization of catalysts and substrates, kinet-
ics and reaction procedures, additional Schemes, Figure and
Tables, and data collection for the crystal structure of com-
plex 1 for this article are available as Supporting Informa-
tion.
Experimental Section
Acknowledgements
Typical Hydroamination Procedure for Terminal
Alkynes (Table 1, entry 3)
A. L. thanks CSIC for a contract under JAE-doctors pro-
gram. Financial support by MAT2006-14274-CC0201,
PROMETEO from Generalitat Valenciana and Fundaciꢀn
Areces are acknowledged.
Complex 1 (89 mg, 5 mol%) and p-toluidine 4 (216 mg,
2 mmol) were placed in a round-bottomed flask and air was
evacuated. Nitrogen refilling was carried out, a rubber
septum was rapidly fitted and a nitrogen balloon was cou-
pled through a needle. Then, CH2Cl2 (2 mL) and 1-octyne 3
(355 mL, 2.4 mmol) were sequentially added and the mixture References
was magnetically stirred at room temperature for 24 h. n-
Hexanes (100 mL) were added, observing the rapid precipi-
tation of the solid. The mixture was magnetically stirred for
15–30 min (alternatively, in some cases, it was left into a
fridge at À148C to assure a quantitative precipitation). The
liquid was passed through a filter containing a Celiteꢂ layer
on top. The solid was washed with n-hexanes and the liquid
was filtered again. The filtrates were concentrated under re-
duced pressure and, after drying under vacuum the resulting
residue, (1-methylheptylidene)-p-tolylamine 6 (E:Z=4:1)
was obtained; yield: 321 mg (74%). GC/MS: major peaks
found at m/z=217 (M+·), 160, 148, 147, 132, 106, 91;
1H NMR: d=7.10 (2H, d, J=8 Hz), 6.60 ( 2H, d, J=8 Hz),
2.40 (2H, t, J=8 Hz), 2.35 (3H, s), 1.75 (3H, s), 1.65 (2H,
quint), 1.45–1.3 (6H, mult), 0.95 (3H, t); 13C NMR (signals
corresponding to the minor isomer between brackets): d=
171.9 (172.5), 149.0 (148.5), 132.0 (131.9), 129.2 (ꢃ2), 119.3
[1] For reviews see: a) F. Alonso, I. P. Beletskaya, M. Yus,
Chem. Rev. 2004, 104, 3079; b) T. E. Mꢄller, K. C.
Hultzsch, M. Yus, F. Foubelo, M. Tada, Chem. Rev.
2008, 108, 3795.
[2] For additional reviews see: a) R. Severin, S. Doye,
Chem. Soc. Rev. 2007, 36, 1407; b) F. Pohlki, S. Doye,
Chem. Soc. Rev. 2003, 32, 104; c) I. Aillaud, J. Collin, J.
Hannedouche, E. Schulz, Dalton Trans. 2007, 5105. For
a review about gold-catalysed hydroaminations, see:
d) R. A. Widenhoefer, X. Han, Eur. J. Org. Chem.
2006, 4555.
[3] a) A. Heutling, S. Doye, J. Org. Chem. 2002, 67, 1961;
b) E. Haak, I. Bytschkov, S. Doye, Angew. Chem. 1999,
111, 3584; Angew. Chem. Int. Ed. 1999, 38, 3389; c) F.
Pohlki, I. Bytschkov, H. Siebeneicher, A. Heutling,
W. A. Kçnig, S. Doye, Eur. J. Org. Chem. 2004, 1967.
Adv. Synth. Catal. 2009, 351, 2876 – 2886
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