Communication
RSC Advances
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Scheme 4 The gram scale experiment.
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4 Selected recent examples for synthesising indolizines: (a)
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Scheme 5 The proposed mechanism.
solubility of potassium dichromate in DMF. 9 and 8 are thus
generated from 7 by hydrogen abstraction. The dipolar species 9
would readily react with alkene 4 through 1,3-dipolar cycload-
dition to form intermediate 10, followed by dehydrogenative
aromatization promoted by 8 or 11. Since 8 and 11 contain the
same anion with TPCD and TPND which are known to oxidize
10, they are proposed to oxidize 10 to 5 and reduced to Cr(III)
species.5 The proposed mechanism is consistent with our
experimental result.
Conclusions
A one-pot method for the synthesis of multi-substituted indo-
lizines was developed, starting from a-halo-carbonyl
compounds, pyridines and electron decient alkenes. In this
method, sub-equivalent amount of potassium dichromate was
used as an oxidant under base free conditions, which rendered
this transformation economically efficient. The substrate
scopes of this method were broad, since various electron de-
cient alkenes, pyridines and a-halo-carbonyl compounds were
successfully applied in this stage. At last, the synthetic utility
has been successfully raised up to a practical gram scale, which
may attract the interests of many medicinal and material
chemists.
Acknowledgements
We are grateful to funding of NSFC (no.: 21202058, 21401063),
Education Department of Jiangsu Province (no. 13KJA150001),
CPSF (no.: 2012M511645, 2013T60483), MOE (no. 13zs1102)
and CSCSE (no. 13zs1102) for their nancial supports.
Notes and references
1 (a) W. Flisch, in Comprehensive Heterocyclic Chemistry, ed. A.
R. Katritzky and C. W. Rees, Pergamon, Oxford, 1984, vol. 4,
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