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Date: 26-03-15 17:59:10
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Allylation of Isatins
Scheme 4. Allylation of N-protected isatins derived from nitro olefins.
the isatins results in the observed major (R) enantiomer
(Scheme 3).
Acknowledgments
We have also tested the efficacy of the organocatalyst 9
for nitro olefin derived isatins. However, instead of ob-
taining allylation products, we detected structurally interest-
ing 1-substituted 3-allylideneindolin-2-one compounds; but
at this point of time we do not know if these compounds
have any practical use (Scheme 4).
The authors are thankful to the Council of Scientific and Industrial
Research (CSIR) and the CSIR-Indus Magic Project (CSC0123)
for financial support. D. G. is thankful to the Academy of Scientific
and Innovative Research (AcSIR) for a Ph.D. enrollment. Analyti-
cal Discipline and Centralized Instrumental Facility is gratefully
acknowledged for providing instrumental facilities.
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Conclusions
We have developed a series of new squaramide-based
organocatalysts among which catalyst 9 showed very good
catalytic efficiency in the asymmetric allylation reaction of
various isatins with allyltributyltin as allyl source. A
2.5 mol-% loading of the organocatalyst is sufficient to give
the corresponding 3-allyl-3-hydroxyoxindoles in high yields
with enantioselectivities of up to 98% ee. An attempt for
the allylation of N-protected isatins derived from nitro
olefins was also made, which gave substituted allylidene-
indolin-2-ones instead of the expected allylated products.
Further work in this direction is currently in progress in our
laboratory to further expand the scope of the organocata-
lyst thus developed.
Experimental Section
General Procedure for the Catalytic Asymmetric Allylation of Isatins
with Allyltributyltin by Using 9 as Organocatalyst: In an oven-dried
5 mL glass flask were placed catalyst 9 (7 mg, 0.0125 mmol) and
isatin (0.5 mmol), and DCM (2 mL) was added. The reaction mix-
ture was then cooled to –20 °C. Allyltributyltin (1.2 equiv. with re-
spect to isatin) was added dropwise. The resulting mixture was
stirred at this temperature until the reaction was complete as indi-
cated by TLC. The reaction was quenched with distilled H2O and
the mixture extracted with EtOAc. The combined organic layers
were washed with H2O, saturated aqueous NaCl solution, dried
with anhydrous Na2SO4 and concentrated under vacuum. The
products were purified by flash chromatography on silica gel. Prod-
ucts were identified by NMR spectroscopic data corresponding to
those published.
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Supporting Information (see footnote on the first page of this arti-
cle): Experimental details, characterization data of both catalysts
1
and substrates, HPLC profile of the products and copies of the H
and 13C NMR spectra of all new catalysts and products.
Eur. J. Org. Chem. 0000, 0–0
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