C O M M U N I C A T I O N S
Table 2. CuI-Catalyzed Coupling of 2-Iodotrifluoroacetanilides and
°C through a combination of ortho substitution and ligand and
solvent effects. This represents the lowest reaction temperature for
Ullmann-type reactions so far. The excellent enantioselectivity
provided evidence for the participation of the Cu(I)-amino acid
chelate in the transition state of the reaction. This observation is
expected to be useful for mechanistic studies of Ullmann-type
reactions.14 In addition, the inexpensive catalytic system makes this
asymmetric coupling reaction valuable for organic synthesis. For
example, compound 5d may serve as an ideal intermediate to
assemble physostigmine and related natural products.2,5,15 Further
exploration on the scopes and limits of the synthetic application
are in progress.
2-Methylacetoacetatesa
Acknowledgment. We are grateful to the Chinese Academy
of Sciences, National Natural Science Foundation of China (Grants
20321202 and 20572119) and Science and Technology Commission
of Shanghai Municipality (Grants 02JC14032 and 03XD14001) for
their financial support.
Supporting Information Available: Experimental and spectral data
for all new compounds. This material is available free of charge via
References
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a Reaction conditions: iodide (0.5 mmol), â-keto ester (0.75 mmol), CuI
(0.1 mmol), trans-4-hydroxy-L-proline (0.2 mmol), NaOH (2 mmol), DMF
(1 mL), H2O (5 µL). b Isolated yields. c Determined by chiral HPLC. d 5
mmol of NaOH was added. e Reductive coupling product was isolated in
22% yield.
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Palucki, M.; Buchwald, S. L. J. Am. Chem. Soc. 1998, 120, 1918. (b)
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Scheme 1. Conversion of 5a to oxindole 8
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(10) Cai, Q.; Zou, B.; Ma, D. Angew. Chem., Int. Ed. 2006, 45, 1276.
(11) Adding 23 µL (0.1 mmol) of t-BuOH gave the almost identical result.
The role for these additives is not clear. For similar observations, see:
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38, 1570. (b) Dosa, P. I.; Fu, G. C. J. Am. Chem. Soc. 1998, 120, 445. (c)
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14043.
813 as depicted in Scheme 1. Baeyer-Villiger oxidation of 5a with
mCPBA under solvent-free conditions produced ester 7, which was
treated with aqueous K2CO3 in MeOH to afford 8. By comparing
27
the rotation of our synthetic 8 ([R]D +46 (c 0.63, MeOH) with
that reported for (R)-8 ([R]D27 +50 (c 1.0, MeOH)),13 we concluded
that the configuration of our coupling products is S.
In conclusion, we have found that CuI-catalyzed coupling
between aryl iodides and â-keto esters can be performed at -45
JA066991J
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J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006 16051