C O M M U N I C A T I O N S
Table 2. Scope of the Gold-Catalyzed Homogeneous Oxidative
phenylboronic acid facilitated by the formation of a strong B-F bond.
Alternatively, Ph3PAuPh10 could be initially formed via transmetala-
tion11 and then oxidized, which may help explain the result shown in
Table 1, entry 5. The thus-generated cationic complex C would then
activate the alkene toward tosylamide attack. The lack of total
stereoselectivity (stereospecificity) is likely due to some double bond
isomerization during the reaction.
Carboheterofunctionalization of Alkenesa
In conclusion, we have developed carboamination, carboalkoxylation
and carbolactonization of terminal alkenes via oxidative gold catalysis,
providing expedient access to various substituted N- or O-heterocycles.
Deuterium-labeling studies established the anti nature of the alkene
functionalization and the indispensable role of Au(I)/Au(III) catalysis.
This study constitutes the first example of catalytically converting
C(sp3)-Au bonds into C(sp3)-C(sp2) bonds in a cross-coupling
manner and opens new opportunities to study gold alkene catalysis
where alkylgold intermediates can be readily functionalized.
Acknowledgment. We thank NSF (CAREER award CHE-
0969157) and UCSB for generous financial support.
Note Added after ASAP Publication. Reference 6 was changed
on January 12, 2010.
Supporting Information Available: Experimental procedures,
compound characterization data. This material is available free of charge
References
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Scheme 2. Proposed Reaction Mechanism
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labeled with deuterium at the unsubstituted end of the C-C double
bond was subjected to the reaction. As shown in eq 1, from
sulfonamide (E)-4f-d, no deuterium loss was detected, and moreover,
excellent diastereoselectivity was observed; similarly, with (Z)-4f-d,
there was no deuterium loss and the other diastereomer (i.e., 6′, eq 2)
was formed highly selectively. The relative stereochemistries were
established on the basis of conformation analysis and 1H-1H coupling
constants. These results revealed an anti addition of the sulfonamide
and the phenyl group to the C-C double bond.
The above deuterium-labeling studies offered important insights for
the proposed reaction mechanism (Scheme 2 using eq 1 as an example):
(a) the initial attack by the sulfonamide to the gold-activated alkene
should be anti, consistent with literature precedents,2b,6 and a syn attack
followed by a configuration inversion of the gold-bound carbon center
via an SN2 process is highly unlikely; (b) the formation of the
C(sp3)-Ph bond (i.e., from E to 6) must involve a concerted reductive
elimination; a radical mechanism is unlikely. This concerted process
demands a central role of gold in mediating the C-C bond formation
and necessitates oxidation of Au(I) to Au(III) by an external oxidant
in the catalytic cycle. Although Ph3PAuCl is unlikely to be the metal
complex promoting the amide anti attack, it could be oxidized by
Selectfluor to Au(III) B, which might undergo transmetalation with
(10) Indeed, Ph3PAuPh (5 mol %) catalyzed this reaction rather efficiently (86%
NMR yield, 60 °C, 2 h).
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Int. Ed. 2006, 45, 8188–8191. (b) Hashmi, A. S. K.; Ramamurthi, T. D.;
Rominger, F. J. Organomet. Chem. 2009, 694, 592–597.
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