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releases the Lewis acid catalyst to yield the minor product 4a.
During the reaction, D can also be decomposed to 4b,12 which
was successfully isolated and identified.
In summary, iron-catalyzed alkylation of a-oxo ketene dithio-
acetals was realized by using styrenes as the alkylating reagents.
Highly functionalized olefin derivatives were prepared in moderate
to good yields, demonstrating an alternative route to tetrasubsti-
tuted olefins.
This work was financially supported by the National Natural
Science Foundation of China (21272232).
Fig. 1 Molecular structure of compound 6e.
Notes and references
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Scheme 2 Proposed mechanism.
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´
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yields, whereas the acyclic substrates reacted slowly to produce
6d (36%) and 6e (32%). The molecular structure of 6e was further
confirmed by the X-ray crystallographic determination (Fig. 1).
Further transformations of the alkylation products were carried
out by Suzuki cross-coupling reactions of 3k and 5i (eqn (2)). They
reacted with p-tolylboronic acid to form 7a (64%) and 7b (56%),
respectively, suggesting a potential application in the preparation
of highly functionalized tetrasubstituted olefins.
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A plausible mechanism is proposed in Scheme 2. Initially,
interaction of the iron(III) catalyst FeX3 with styrene (2a) forms
benzylic carbocation A, which is then trapped by a-EWG ketene
dithioacetal 1a to form a more stable carbocation species B
stabilized by the two adjacent thioalkyls.8d Regeneration of the
´
catalyst from B affords the target product 3a. Iron(III) species A 12 (a) J. R. Cabrero-Antonino, A. Leyva-Perez and A. Corma, Adv. Synth.
can also activate the soft nucleophile, that is, a styrene,2c pro-
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J. T. Wang, H. J. Li and L.-M. Wu, Org. Lett., 2011, 13, 2208;
(c) R. Sanz, D. Miguel, A. Martınez, J. M. Alvarez-Gutierrez and
F. Rodrıguez, Org. Lett., 2007, 9, 2027.
ducing carbocation D by insertion of the alkene to its C–Fe
bond. Subsequent reaction with 1a gives intermediate E, which
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Chem. Commun., 2014, 50, 6337--6339 | 6339