2344
Y. Uenoyama et al.
CLUSTER
O
Br
AIBN (30 mol%)
+
SnBu3
2.5 equiv
+ CO
+
CO2Et
1.4 equiv
C6H6
80 atm, 80 °C, 12 h
CO2Et
1d 0.03 M
2i
60% (54/46)
Equation 9
CO
References and Notes
Br
CO
(1) (a) Ryu, I.; Kusano, K.; Hasegawa, M.; Kambe, N.; Sonoda,
N. J. Chem. Soc., Chem. Commun. 1991, 1018. (b) Curran,
D. P.; Liu, H. J. Am. Chem. Soc. 1991, 113, 2127.
(c) Tsunoi, S.; Ryu, I.; Yamasaki, S.; Fukushima, H.;
Tanaka, M.; Komatsu, M.; Sonoda, N. J. Am. Chem. Soc.
1996, 118, 10670. (d) Ryu, I.; Nagahara, K.; Kurihara, A.;
Komatsu, M.; Sonoda, N. J. Organomet. Chem. 1997, 548,
105. (e) Ryu, I.; Nagahara, K.; Yamazaki, H.; Tsunoi, S.;
Sonoda, N. Synlett 1994, 643. (f) Tsunoi, S.; Ryu, I.;
Fukushima, H.; Tanaka, M.; Komatsu, M.; Sonoda, N.
Synlett 1995, 1249. (g) Curran, D. P.; Sisko, J.; Balog, A.;
Sonoda, N.; Nagahara, K.; Ryu, I. J. Chem. Soc., Perkin
Trans. 1 1998, 1591. (h) Tsunoi, S.; Ryu, I.; Yamazaki, S.;
Tanaka, M.; Sonoda, N.; Komatsu, M. Chem. Commun.
1997, 1889.
Bu3Sn
O
O
O
CO2Et
SnBu3
6-endo
5-exo
CO2Et
nucleophilic
electrophilic
O
O
SnBu3
β-fission
CO2Et
CO2Et
SnBu3
Bu3Sn
CO2Et
newly formed C-C bond
(2) For reviews on radical carbonylations, see: (a) Ryu, I.;
Sonoda, N. Angew. Chem., Int. Ed. Engl. 1996, 35, 1050.
(b) Ryu, I.; Sonoda, N.; Curran, D. P. Chem. Rev. 1996, 96,
177. (c) Ryu, I. Chem. Soc. Rev. 2001, 30, 16. (d) See also a
review on acyl radicals: Chatgilialoglu, C.; Crich, D.;
Komatsu, M.; Ryu, I. Chem. Rev. 1999, 99, 1991.
(3) For a 6-endo reaction using a Zn-induced system, see ref. 1h.
(4) (a) Ryu, I.; Yamazaki, H.; Kusano, K.; Ogawa, A.; Sonoda,
N. J. Am. Chem. Soc. 1991, 113, 8558. (b) Ryu, I.;
Yamazaki, H.; Ogawa, A.; Kambe, N.; Sonoda, N. J. Am.
Chem. Soc. 1993, 115, 1187. (c) Nagahara, K.; Ryu, I.;
Yamazaki, H.; Kambe, N.; Komatsu, M.; Sonoda, N.; Baba,
A. Tetrahedron 1997, 53, 14615. (d) Ryu, I.; Niguma, T.;
Minakata, S.; Komatsu, M.; Luo, Z.; Curran, D. P.
Tetrahedron Lett. 1999, 40, 2367.
Scheme 2 Preferred radical reaction pathway for four-component
cascade reaction.
In summary, the consecutive carbonylation and 6-endo
cyclization sequence of 4-substituted 4-pentenyl radicals
to give 1-substituted 3-oxo-cyclohexyl radicals was suc-
cessfully coupled with the subsequent alkene addition re-
actions. By using this cascade radical carbonylation
strategy, 3-substituted and 3,3-disubstituted cyclohex-
anones were prepared successfully.
Acknowledgment
(5) (a) Keck, G. E.; Enholm, E. J.; Yates, J. B.; Wiley, M. R.
Tetrahedron 1985, 41, 4079. (b) Mizuno, K.; Ikeda, M.;
Toda, S.; Otsuji, Y. J. Am. Chem. Soc. 1998, 110, 1288.
(c) Curran, D. P.; van Elburg, E. J.; Giese, B.; Gilges, S.
Tetrahedron Lett. 1990, 31, 2861. (d) Curran, D. P.; Xu, J.;
Lazzarini, E. J. Chem. Soc., Perkin Trans. 1 1995, 3049.
(6) The reaction also gave the product via a 5-exo/allylation
sequence in 5% yield. At higher CO pressures, the second
carbonylation of the 5-exo-radical also took place. Details
will be discussed in a full paper.
I.R. acknowledges a Grant-in-Aid for Scientific Research on Priori-
ty Areas ‘Advanced Molecular Transformations of Carbon Re-
sources’ from MEXT Japan. Y.U. acknowledges a Grant-in-Aid
from JSPS scholarship. We thank Hiroshi Yamasaki, Hiroshi Fu-
kushima, and Fumikazu Araki at Osaka University for initial expe-
rimental work.
(7) 3-Allyl-3-methylcyclohexanone (2d)
A magnetic stirring bar, AIBN (26.2 mg, 0.16 mmol),
benzene (3.4 mL), 4-methyl-4-pentenyl bromide (1d; 92.3
mg, 0.56 mmol), and allyltributyltin (400.0 mg, 1.2 mmol)
were placed in a 50-mL stainless-steel autoclave. The
autoclave was closed, purged three times with CO,
pressurized with 50 atm of CO, and then heated at 80 °C for
12 h. Excess CO was discharged at r.t. The solvent was
removed under reduced pressure. The residue was purified
by flash chromatography on silica gel (hexane→hexane–
EtOAc, 10:1) to give 3-allyl-3-methylcyclohexanone (2d;
73.3 mg, 85%).
Synlett 2006, No. 14, 2342–2344 © Thieme Stuttgart · New York