LETTER
Asymmetric Michael Addition with Chiral Multisite Phase-Transfer Catalysts
1691
Rodríguez, A.; Sánchez-Verdú, P. Tetrahedron 1998, 54,
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1.
electrophile with a carbocation of the chalcone due to
electrostatic attraction14 and also the same attraction be-
tween the R4N+ of the respective CMPTC with enolate of
the chalcone (Figure 4, b). The results also suggested that
apart from the ionic interaction between the catalyst and
substrates, there is also a π–π-stacking interaction15 be-
tween the benzyl group of the respective C9(O)-protected
CMPTC with the aryl group of the chalcone which would
further facilitate the binding of the two species. This in
turn shows to facilitate an effective ion-pair interaction
and thus effect for parallel increasing of chemical yield
and enantiomeric excesses.
(9) A mixture of 2,4,6-tris-(4-bromomethylphenyl)-[1,3,5]triazine
(9, 0.1 g, 10 mmol), cinchona derivatives 10a or 10b (30
mmol) was dissolved in THF (5 mL) and heated to reflux
overnight, the white solid was filtered, washed with Et2O,
and dried to get pure three-site chiral phase-transfer catalyst
(86% yield).
In conclusion, we have developed a new class of asym-
metric phase-transfer catalyst, which shows good enanti-
oselectivity in the Michael addition of diethyl malonate to
chalcones. We are currently involved in the further devel-
opment of these catalyst systems and investigating their
applicability to other asymmetric phase-transfer process-
es.
Triazine-Based Benzylcinchonine (11a)
1H NMR (400 MHz, DMSO-d6): δ = 9.08 (s, 1 H), 8.97 (d, J
= 7.5 Hz, 2 H), 8.48–8.37 (m, 1 H), 8.20 (d, J = 8.2 Hz, 1 H),
8.14 (d, J = 8.0 Hz, 1 H), 8.04–7.98 (m, 1 H), 7.97–7.91 (m,
1 H), 7.86 (d, J = 9.6 Hz, 2 H), 7.62 (d, J = 7.3 Hz, 2 H), 7.51
(dd, J = 20.1, 12.4 Hz, 2 H), 7.42 (dd, J = 12.7, 5.5 Hz, 1 H),
6.67–6.51 (m, 1 H), 6.07–5.83 (m, 1 H), 5.80 (dd, J = 22.9,
13.5 Hz, 1 H), 5.29 (d, J = 11.4 Hz, 1 H), 5.20–5.13 (m, 1 H),
5.10–4.91 (m, 2 H), 4.85–4.69 (m, 1 H), 4.66–4.53 (m, 1 H),
4.51–4.29 (m, 1 H), 4.10 (s, 2 H), 2.68 (s, 2 H), 2.11–1.90
(m, 2 H), 1.82 (d, J = 12.0 Hz, 2 H), 1.27 (s, 1 H). 13C NMR
(125 MHz, DMSO-d6): δ = 171.49, 150.8, 148.58, 141.57,
140.86, 138.26, 137.58, 137.36, 137.23, 135.08, 130.35,
130.21, 130.08, 129.6, 129.23, 128.97, 128.93, 128.85,
128.72, 128.58, 128.42, 128.33, 128.07, 117.16, 116.85,
116.12, 71.22, 70.97, 70.86, 68.48, 59.46, 37.32, 27.04,
26.38, 24.69. ESI-MS: m/z = 1765.00 [M]3+.
Acknowledgment
We acknowledge the financial support of the University Grants
Commission, New Delhi, India (Grant No. UGC No.41-215/2012
(SR) and Council of Scientific and Industrial Research, New Delhi,
India [Grant No. 01(2540)/11/EMR-II].
Supporting Information for this article is available online
at
Triazine-Based Allylcinchonine (11b)
10.1055/s-00000083.SunpfgIpi
o
o
nr
i
1H NMR (500 MHz, DMSO-d6): δ = 9.06 (d, J = 3.9 Hz, 1
H), 8.96 (d, J = 6.7 Hz, 2 H), 8.44 (d, J = 7.5 Hz, 1 H), 8.17
(d, J = 8.2 Hz, 1 H), 8.15–8.08 (d, J = 6.7 Hz, 2 H), 7.91 (d,
J = 7.8 Hz, 1 H), 7.85–7.81 (m, 1 H), 7.74 (s, 1 H), 6.46 (s,
1 H), 6.29–6.19 (m, 1 H), 6.04 (dd, J = 17.2, 6.7 Hz, 1 H),
5.50 (d, J = 17.4 Hz, 1 H), 5.37 (d, J = 10.0 Hz, 1 H), 5.27 (t,
J = 13.5 Hz, 2 H), 4.82 (s, 1 H), 4.35 (d, J = 7.1 Hz, 1 H),
4.17 (d, J = 22.3 Hz, 2 H), 4.05 (s, 2 H), 3.66 (d, J = 9.9 Hz,
1 H), 3.06 (s, 2 H), 2.70 (s, 1 H), 1.95 (s, 1 H), 1.81 (s, 3 H),
1.25 (s, 1 H). 13C NMR (125 MHz, DMSO-d6): δ = 171.53,
150.65, 148.45, 141.16, 137.43, 137.26, 135.17, 134.66,
133.24, 130.21, 129.64, 128.0, 125.66, 124.58, 120.27,
118.49, 117.58, 73.55, 69.95, 67.55, 62.94, 56.71, 54.98,
37.0, 26.77, 23.28, 21.61. ESI-MS: m/z = 1599.9200 [M]3+.
(10) Singh, P.; Arora, G. Indian J. Chem., Sect. B: Org. Chem.
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1685–1691