Communications
hindered p face of the allene 1, and this possibility cannot be
completely excluded at present.
In conclusion, we have developed a gold-catalyzed
intermolecular hydroamination of allenes, which proceeds
smoothly at room temperature. In this reaction, the axial
chirality of allenes is transferred to the products through the
hydroamination to give high ee values.
Received: January 26, 2006
Published online: April 18, 2006
Keywords: allenes · allylic compounds · gold · hydroamination
.
[1] For recent reviews of catalytic hydroamination, see: a) T. E.
Müller, M. Beller, Chem. Rev. 1998, 98, 675 – 703; b) J. J. Brunet,
D. Neibecker in Catalytic Heterofunctionalization (Eds.: A.
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lanthanides, see: S. Hong, T. J. Marks, Acc. Chem. Res. 2004, 37,
673 – 686.
Scheme 1. Chiralitytransfer in the hydroamination of allenes.
A plausible mechanism, though speculative, is shown in
Scheme 2. The catalytic cycle is most probably initiated by the
coordination of the allene to the gold–amine complex B to
afford the intermediate C. The presence of the gold–amine
[3] For a recent reviewof base-catalyzed hydroamination, see: a) J.
Seayad, A. Tillack, C. G. Hartung, M. Beller, Adv. Synth. Catal.
2002, 344, 795 – 813; for recent examples of acid-catalyzed
hydroamination, see: b) B. Schlummer, J. F. Hartwig, Org. Lett.
2002, 4, 1471 – 1474; c) K. Miura, A. Hosomi, Synlett 2003, 143 –
155.
[4] For recent reviews of hydroamination catalyzed by early
transition metals, see: a) I. Bytschkov, S. Doye, Eur. J. Org.
Chem. 2003, 935 – 946; b) S. Doye, Synlett 2004, 1653 – 1672;
c) A. L. Odom, Dalton Trans. 2005, 225 – 233.
[5] For recent examples of hydroamination catalyzed by late
transition metals, see: a) H. M. Senn, P. E. Blöchl, A. Togni, J.
Am. Chem. Soc. 2000, 122, 4098 – 4107; b) T. E. Müller, M.
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Scheme 2. A plausible mechanism for the hydroamination of 1.
complex is postulated based on the fact that there was an
induction period for the hydroamination, and the yield was
decreased when AuBr3 was not exposed to the amine prior to
the addition of allene. It should be noted that the 1,1-
disubstituted allenes 1i and 1k exhibited extremely low
reactivities. This is in marked contrast to the palladium-
catalyzed hydroamination of 1,1-disubstituted allenes, which
proceeded smoothly via a p-allylpalladium intermediate.[19]
Consequently, the gold-catalyzed hydroamination must pro-
ceed in a manner different from the palladium-catalyzed
reaction. Perhaps the amino-auration takes place through C
to give the gold–alkenyl intermediate D, which produces 3
and AuBr3 upon protonation by HBr. It may be argued that D
should afford Z allylamines instead of the E isomers 3. One
explanation for the observation of the E isomers is that the
isomerization may take place through the intermediate E.
However, formation of the E allylamines is alternatively
explainable by the attack of the gold species at the more
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Arredondo, S. Tian, F. E. McDonald, T. J. Marks, J. Am. Chem.
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Angew. Chem. Int. Ed. 2006, 45, 3314 –3317