LETTER
Carbon-Carbon Bond Forming Reactions In Supercritical Carbon Dioxide
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(5) For recent reviews, see: Savage, P.E.; Gopalan, S.; Mizan,
T.I.; Martino, C.J.; Brock, E.E. AIChE J. 1995, 41, 1723;
Kaupp, G. Angew. Chem. Int. Ed. Engl. 1994, 33, 1452.
(6) For a few recent leading references on the utilization of scCO2
as a reaction medium alternative to normal organic solvents
for catalytic reactions with transition metal complexes, see:
Carrol, M.A.; Holmes, A.B. Chem. Commun., 1998, 1395;
Morita, D.K.; Pesiri, D.R.; David, S.A.; Glaze, W.H.; Tumas,
W. Chem. Commun., 1998, 1397; Kainz, S.; Koch, D.;
Baumann, W.; Leitner, W. Angew. Chem. Int. Ed. Engl. 1997,
36, 1628. Xiao, J.; Nefkens, S.C.A.; Jessop, P.G.; Ikariya, T.;
Noyori, R. Tetrahedron Lett. 1996, 37, 2813. Jessop, P.G.;
Hsiao, Y.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1996,
118, 344. Kröcher, O.; Köppel, R.A.; Baiker, A. Chem.
Commun. 1996, 1497; Burk, M.J., Feng, S.; Gross. M.F.;
Tumas, W. J. Am. Chem. Soc. 1995, 117, 8277.
(7) Solubility measurements of the reactants were performed
using a 50 mL reactor with an additional sample port connec-
ted to a Rheodyne 7010 sample injector six port valve equip-
ped with a 0.75 mL, thermostated, sample loop. Samples were
withdrawn from the uppermost phase of the reactor and direc-
ted into the loop: after pressure equilibration, the loop was de-
pressurized into a 50 x 4 mm column packed with ODS silica.
The loop and the column were washed with CH2Cl2, the wa-
shings made up to volume in a volumetric flask and analyzed
by GC or HPLC. For example, the solubility of PhI was found
to be 1.22 mg/mL, while butenone, and Et3N, in the amounts
employed, are completely soluble.
mode. After heating the reaction mixture for 60 h, the reactor
was cooled to room temperature and slowly depressurized
through a capillary tube immersed in 30 mL of diethylether.
The reaction mixture was diluted with additional diethylether
and the combined solutions were placed in a separatory fun-
nel, washed with 0.1 N HCl, sat. NaHCO3 and saturated NaCl,
dried over Na2SO4 and concentrated under reduced pressure.
The residue was purified on an axially compressed column
(packed with 35 g of SiO2 25-40 mm - Macherey Nagel - con-
nected to a Gilson solvent delivery system and to a Gilson re-
fractive index detector) eluting with a n-hexane/EtOAc 95/5
(v/v) mixture to give 0.091 g (64% yield) of benzalacetone
and 0.017 g (12% yield) of 4-phenyl-2-butanone; oil; IR (neat)
1717, 750, 700 cm-1; 1H NMR d 7.33-7.12 (m, 5H), 2.95–2.83
(m, 2H), 2.82–2.69 (m, 2H), 2.13 (s, 3H); 13C NMR d 208.0,
141.0, 128.5, 128.3, 126.1, 45.2, 30.1, 29.7; MS m/e (relative
intensity) 148 (M+, 7), 133 (43), 105 (80), 43 (100).
(9) For other palladium-catalyzed hydroarylation (formal conju-
gate addition) reactions of a,b-unsaturated carbonyl com-
pounds and aryl halides, see: a) Hagiwara, H.; Eda, Y.;
Morohashi, K.; Suzuki, T.; Ando, M.; Ito, N. Tetrahedron
Lett. 1998, 39, 4055; b) Arcadi, A.; Cacchi, S.; Fabrizi, G.;
Marinelli, F.; Pace, P. Tetrahedron 1996, 52, 6983;
c) Friestad, G.K.; Branchaud, B.P. Tetrahedron Lett. 1995, 36,
7047; d) Benhaddou, R.; Czernecki, S.; Ville, G. J. Org.
Chem. 1992, 57, 4612; e) Konopelski, J.P.; Chu, K.S.; G.R.
Negrete, G.R. J. Org.Chem. 1991, 56, 1355; f) Cacchi, S. Pure
& Appl. Chem. 1990, 62, 713; g) Amorese, A.; Arcadi, A.;
Bernocchi, E.; Cacchi, S.; Cerrini, S.; Fedeli, W.; Ortar, G.
Tetrahedron 1989,45, 813; h) Hoffman, H.M.R.; Schmidt, B.;
Wolff, S. Tetrahedron 1989, 45, 6113; i) Wada, A.; Ohki, K.;
Nagai, S.; Kanatomo, S. J. Heterocycl. Chem. 1991, 28, 509;
j) Stokker, G.E. Tetrahedron Lett. 1987, 28, 3179; k) Cacchi,
S.; Arcadi, A. J. Org. Chem. 1983, 48, 4236.
(8) Typical procedure for the palladium-catalyzed reaction of aryl
iodides with alkenes. A 50 mL stainless steel reactor charged
with phenyl iodide (0.200 g, 0.980 mmol), 3-buten-2-one
(0.244 mL, 2.94 mmol), triethylamine (0.296 g, 2.94 mmol)
and palladium on activated carbon 10 % w/w (0.104 g, 0.098
mmol) was placed in a preheated (80°C) aluminum block. The
reactor was initially pressurized to 85 bar with CO2 and after
thermal equilibration (10 min) to 100 bar using a Carlo Erba
Mod SFC 300 syringe pump operating in the constant pressure
(10) Laschat, S.; Narjes, F.; Overman, L.E. Tetrahedron 1994, 50,
347; Cabri, W.; Candiani, I.; De Bernardis, S.; Francalanci, F.;
Penco, S. J. Org. Chem. 1991, 56, 5796.
Synlett 1999, No. 3, 345–347 ISSN 0936-5214 © Thieme Stuttgart · New York