C O M M U N I C A T I O N S
Table 3. Decarboxylative Coupling of Heterocyclic Alkyl-Allyl
Scheme 1
Estersa
Crystallization and analysis via single-crystal X-ray diffraction
revealed a cis-configuration of the C-2 and C-3 centers (4g, Scheme
1). This stereochemistry suggests a boat-like transition state
involving the E,E-geometry of C. It has been suggested that certain
cyclic substrates are more apt to undergo [3,3]-sigmatropic re-
arrangements via a boat transition state in an effort to relieve steric
strain imposed by the chair conformation.15
In conclusion, we have demonstrated a tandem allylation/aza-
Cope rearrangement strategy for the diastereoselective sp3-sp3
coupling of allyl electrophiles and heteroaromatic alkanes. To the
best of our knowledge, this is the first report of a tandem allylation/
aza-Cope reaction that is driven by decarboxylative dearomatization/
rearomatization.
Acknowledgment. We thank the National Science Foundation
(CHE-0548081) and the Petroleum Research Fund (44453-AC1).
We also thank Victor Day for the X-ray crystallographic analysis.
Supporting Information Available: Experimental procedures and
characterization data for all new compounds. This material is available
a 0.25 mmol substrate was treated with 0.013 mmol Pd(PPh3)4 in toluene
at 100 °C. b Isolated yields. c Reaction run at 80 °C. d branched:linear (b:
l) ) 93:7. e b:l ) 94:6. f b:l ) 95:5.
amount of several Lewis acids [Sc(OTf)3, PdCl2(CH3CN)2, Cu-
(OAc)2] failed to effect any reaction of 1g at 80 °C in tol-d8 after 16 h.
Also, both 1r and 1h produce 2h as the major product which is
suggestive of a common Pd-π-allyl intermediate (eq 2).
In fact, observation of this reaction by 1H NMR spectroscopy
revealed complete isomerization of the substrate (1r) to the linear
substrate (1h) prior to decarboxylative coupling. Therefore, we
believe that a mechanism involving Pd-π-allyl intermediates is
probable and π-allyl formation is much faster than the formation
of product.
References
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1
of terminal olefinic products akin to 2h (by H NMR). Thus, the
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Following these preliminary mechanistic investigations, we
propose the mechanism shown in Scheme 1. The reaction is initiated
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complex A. At this point, two competing reactions are possible. If
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on the π-allyl complex to produce B. It is important to note that
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observed diastereoselectivity. Related tandem allylation/Cope-
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In order to determine the relative configuration of the product,
compound 2g was treated under conditions for bromocyclization.14
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