IronACHTUNGTRENNUNG(III) Salt-Catalyzed Nazarov Cyclization/Michael Addition of Pyrrole Derivatives
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References
derivatives. The reaction was effectively catalyzed by
5 mol% Fe(ClO4)3·Al2O3 and the desired products
ACHTUNGTRENNUNG
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were obtained in good to excellent yields. Since the
cyclized products reacted with vinyl ketones to give
the corresponding Michael adducts in the presence of
the same iron salt catalyst, a sequential type Nazarov/
Michael reaction has been accomplished. It should be
emphasized that the reaction is accomplished by a
very economical and environmentally friendly iron
salt as catalyst and requires no tedious argon atmos-
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in progress by our group.
Experimental Section
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Synthesis of 5b through the Sequential Type Nazarov
Cyclization/Michael Reaction
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[3,8]
To a mixture of Fe
G
(60 mg, 8.8 wt% for
Fe3+, 0.0125 mmol) in CH2Cl2 (0.5 mL) was added 1a
(64 mg, 0.25 mmol) at room temperature and the mixture
was stirred at 608C for 12 h. The reaction mixture was
cooled to room temperature after confirmation that the
starting 1a had been consumed and 2a produced, then 2
equiv. of but-3-en-2-one (7a) were added to the reaction
mixture at 08C and stirred for 48 h at the same temperature.
The reaction was quenched with water, and the mixture was
extracted with ethyl acetate. The combined organic layers
were dried over anhydrous MgSO4 and concentrated by
evaporation under vacuum. The residue was purified by
preparative silica gel TLC (hexane/ethyl acetate=1/1) to
give 5a as a white solid; yield: 70 mg (0.22 mmol, 86%; 5a
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1
(cis): mp 251–2538C (recrystallized from CHCl3); H NMR
(500 MHz, CDCl3): d=2.18 (3H, s), 2.41–2.48 (1H, m),
2.57–2.65 (2H, m), 2.80–2.87 (1H, m), 3.04 (3H, s), 4.35
(1H, s), 6.15–6.17 (1H, m), 7.14–7.16 (2H, m), 7.23–7.29
(2H, m), 7.42–7.44 (1H, m), 10.94 (1H, brs, N-H); 13C NMR
(125 MHz, CDCl3): d=28.69, 30.01, 38.49, 51.00, 51.39,
71.44, 106.61, 127.51, 127.94, 128.86, 134.05, 134.18, 138.14,
152.62, 170.68, 188.32, 207.93; IR (KBr): n=3293, 1740
(CO), 1711 (CO), 1680 (CO), 1449, 1398, 1381, 1269, 1219,
706 cmÀ1.
Compound 5b was also prepared through the same route
in 87% yield from 1a.
Supporting Information
Detailed experimental procedures and 1H NMR and
13C NMR spectral data for new compounds (2a–2s, 4a, 5a,
5b, and 6a) are available in the Supporting Information.
Acknowledgements
This work was partly supported by a Grant-in-Aid for scien-
tific research from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
Adv. Synth. Catal. 2009, 351, 123 – 128
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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