Abstract
A new protocol for 1,4-conjugate addition of indoles to vinyl ketones has been developed,
employing Lewis acidic ionic liquid immobilized on silica, ILIS-SO2 Cl, as a catalyst, which exhibited an efficient, mild and recyclable nature. The reaction
condition is applicable to various vinyl ketones and indoles. The mild nature of the
reaction condition showed that the acetoxy or TBDMS group in indoles was maintained
intact. The catalyst was used six times resulting in 86% average yield.
Key words
catalysis - Michael additions - indoles - ionic liquids - supported catalysis
References and Notes
<A NAME="RU11507ST-1A">1a </A>
Sundberg RJ.
Indoles
Academic Press;
San Diego:
1996.
<A NAME="RU11507ST-1B">1b </A>
Sundberg RJ.
The Chemistry of Indoles
Academic Press;
New York:
1970.
<A NAME="RU11507ST-2A">2a </A>
Zhou W.
Xu L.-W.
Li L.
Yang L.
Xia C.-G.
Eur. J. Org. Chem.
2006,
5225
<A NAME="RU11507ST-2B">2b </A>
Zhang H.-B.
Liu L.
Liu Y.-L.
Chen Y.-J.
Wang J.
Wang D.
Synth. Commun.
2007,
37:
173
<A NAME="RU11507ST-3A">3a </A>
Loh TP.
Wei LL.
Synlett
1998,
975
<A NAME="RU11507ST-3B">3b </A>
Wang SY.
Ji SJ.
Loh TP.
Synlett
2003,
2377
<A NAME="RU11507ST-3C">3c </A>
Li Z.
Shi Z.
He C.
J. Organomet. Chem.
2005,
690:
5049
<A NAME="RU11507ST-3D">3d </A>
Nayak SK.
Synth. Commun.
2006,
36:
1307
<A NAME="RU11507ST-3E">3e </A>
Huang Z.-H.
Zou J.-P.
Jiang W.-Q.
Tetrahedron Lett.
2006,
47:
7965
<A NAME="RU11507ST-3F">3f </A>
Itoh T.
Uehara H.
Ogiso K.
Nomura S.
Hayase S.
Kawatsura M.
Chem. Lett.
2007,
36:
50
<A NAME="RU11507ST-3G">3g </A>
Yadav JS.
Reddy BVS.
Raju A.
Ravindar K.
Baishya G.
Chem. Lett.
2007,
36:
1056
<A NAME="RU11507ST-3H">3h </A>
Maiti G.
Kundu P.
Synth. Commun.
2007,
37:
2309
<A NAME="RU11507ST-3I">3i </A>
Ambrogio I.
Arcadi A.
Cacchi S.
Fabrizi G.
Marinelli F.
Synlett
2007,
1775; and references cited in these papers
<A NAME="RU11507ST-4A">4a </A>
Kusurkar RS.
Alkobati NAH.
Gokule AS.
Chaudhari PM.
Waghchaure PB.
Synth. Commun.
2006,
36:
1075
<A NAME="RU11507ST-4B">4b </A>
Mohammadpoor-Baltok I.
Memarian HR.
Khosropour AR.
Nikoofar K.
Heterocycles
2006,
68:
1837
<A NAME="RU11507ST-4C">4c </A>
Banik BK.
Garcia I.
Morales FR.
Heterocycles
2007,
71:
919; and earlier references cited in these references
<A NAME="RU11507ST-5">5 </A>
Harrington P.
Kerr MA.
Can. J. Chem.
1998,
76:
1256
<A NAME="RU11507ST-6">6 </A>
Hagiwara H.
Sekifuji M.
Hoshi T.
Qiao K.
Yokoyama C.
Synlett
2007,
1320
<A NAME="RU11507ST-7">7 </A>
Gu Y.
Ogawa C.
Kobayashi S.
Org. Lett.
2007,
9:
175
<A NAME="RU11507ST-8">8 </A>
Qiao K.
Hagiwara H.
Yokoyama C.
J. Mol. Catal. A: Chem.
2006,
246:
65
<A NAME="RU11507ST-9">9 </A>
Typical Experimental Procedure : A suspension of but-3-en-2-one (50 µL, 0.6 mmol), indole (35.3 mg, 0.3 mmol) and
ILIS-SO2 Cl (4 ; 171 mg; loading of sulfonyl chloride: 0.35 mmol/g, 0.06 mmol) in Et2 O (0.2 mL) was stirred gently at ambient temperature for 4 h in open air, resulting
in evaporation of Et2 O. The catalyst was washed with Et2 O and separated by centrifugation. After decantation of the Et2 O layer, the catalyst was washed again with EtOAc and then with CH2 Cl2 in a similar manner. The combined organic layer was evaporated to dryness. Medium
pressure LC of the residue (eluent: EtOAc-n -hexane, 1:1) afforded the conjugated addition product 3 (51.9 mg, 92% based on indole 2 ).
<A NAME="RU11507ST-10A">10a </A>
Laszlo P.
Teston M.
J. Am. Chem. Soc.
1990,
112:
8750
<A NAME="RU11507ST-10B">10b </A>
Leach MR.
In Lewis Acid/Base Reaction Chemistry
Meta-Synthesis;
Brighton, UK:
1999.